Systems and methods for regulating power conversion systems with output detection and synchronized rectifying mechanisms

ABSTRACT

System and method for regulating a power conversion system. A system controller for regulating a power conversion system includes a first controller terminal and a second controller terminal. Additionally, the system controller is configured to receive an input signal at the first controller terminal, and generate a drive signal at the second controller terminal based at least in part on the input signal to turn on or off a transistor in order to affect a current associated with a secondary winding of the power conversion system. Moreover, the system controller is further configured to determine whether the input signal is larger than a first threshold at a first time, in response to the input signal being determined to be larger than the first threshold at the first time, determine whether the input signal is smaller than a second threshold at a second time.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/204,324, filed Jul. 7, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/602,944, filed Jan. 22, 2015, which claimspriority to Chinese Patent Application No. 201410729533.3, filed Dec. 4,2014, all of these applications being incorporated by reference hereinfor all purposes. Additionally, U.S. patent application Ser. No.14/602,944 is a continuation-in-part of U.S. patent application Ser. No.13/466,808, filed May 8, 2012, which claims priority to Chinese PatentApplication No. 201210118202.7, filed Apr. 12, 2012, all of theseapplications being incorporated by reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods with outputdetection and synchronized rectifying mechanisms. Merely by way ofexample, the invention has been applied to a power conversion system.But it would be recognized that the invention has a much broader rangeof applicability.

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system. The power conversion system 100 includes a primarywinding 110, a secondary winding 112, a power switch 120, a currentsensing resistor 122, a rectifying diode 124, a capacitor 126, anisolated feedback component 128, and a controller 102. The controller102 includes an under-voltage-lockout component 104, apulse-width-modulation generator 106, a gate driver 108, aleading-edge-blanking (LEB) component 116, and anover-current-protection (OCP) component 114. For example, the powerswitch 120 is a bipolar transistor. In another example, the power switch120 is a field effect transistor.

The power conversion system 100 implements a transformer including theprimary winding 110 and the secondary winding 112 to isolate an AC inputvoltage 190 on the primary side and an output voltage 192 on thesecondary side. The isolated feedback component 128 processesinformation related to the output voltage 192 and generates a feedbacksignal 136. The controller 102 receives the feedback signal 136, andgenerates a gate-drive signal 130 to turn on and off the switch 120 inorder to regulate the output voltage 192. For example, the isolatedfeedback component 128 includes an error amplifier, a compensationnetwork, and an opto-coupler.

Though the fly-back power conversion system 100 can be used for outputvoltage regulation, the power conversion system 100 often cannot achievegood output current control without additional circuitry of high cost.Moreover, the required output current sensing resistor in the secondaryside usually reduces the efficiency of the power conversion system 100.

FIG. 2(A) is a simplified diagram showing another conventional flybackpower conversion system. The power conversion system 200 includes asystem controller 202, a primary winding 210, a secondary winding 212,an auxiliary winding 214, a power switch 220, a current sensing resistor230, two rectifying diodes 260 and 262, two capacitors 264 and 266, andtwo resistors 268 and 270. For example, the power switch 220 is abipolar transistor. In another example, the power switch 220 is a MOStransistor.

Information related to the output voltage 250 can be extracted throughthe auxiliary winding 214 in order to regulate the output voltage 250.When the power switch 220 is closed (e.g., on), the energy is stored inthe transformer that includes the primary winding 210 and the secondarywinding 212. Then, when the power switch 220 is open (e.g., off), thestored energy is released to the secondary side, and the voltage of theauxiliary winding 214 maps the output voltage on the secondary side. Thesystem controller 202 receives a current sensing signal 272 thatindicates a primary current 276 flowing through the primary winding 210,and a feedback signal 274 that relates to a demagnetization process ofthe secondary side. For example, a switching period of the switch 220includes an on-time period during which the switch 220 is closed (e.g.,on) and an off-time period during which the switch 220 is open (e.g.,off).

FIG. 2(B) is a simplified conventional timing diagram for the flybackpower conversion system 200 that operates in the discontinuousconduction mode (DCM). The waveform 292 represents a voltage 254 of theauxiliary winding 214 as a function of time, and the waveform 294represents a secondary current 278 that flows through the secondarywinding 212 as a function of time.

For example, as shown in FIG. 2(B), a switching period, T_(s) of theswitch 220, starts at time t₀ and ends at time t₃, an on-time period,T_(on), starts at the time t₀ and ends at time t₁, a demagnetizationperiod, T_(demag) starts at the time t₁ and ends at time t₂, and anoff-time period, T_(off), starts at the time t₁ and ends at the time t₃.In another example, t₀≤t₁≤t₂≤t₃. In DCM, the off-time period, T_(off),is much longer than the demagnetization period, T_(demag).

During the demagnetization period T_(demag), the switch 220 remainsopen, the primary current 276 keeps at a low value (e.g., approximatelyzero). The secondary current 278 decreases from a value 296 (e.g., att₁) as shown by the waveform 294. The demagnetization process ends atthe time t₂ when the secondary current 278 has a low value 298 (e.g.,approximately zero). The secondary current 278 keeps at the value 298for the rest of the switching period. A next switching period does notstart until a period of time after the completion of the demagnetizationprocess (e.g., at t₃).

As shown in FIG. 1 and FIG. 2(A), the power conversion system 100 andthe power conversion system 200 each use a rectifying diode (e.g., thediode 124 in FIG. 1 and the diode 260 in FIG. 2 ) on the secondary sidefor rectification. A forward voltage of the rectifying diode is usuallyin a range of 0.3V-0.8V. Such a forward voltage often results insignificant power loss in operation, and thus causes low efficiency ofthe power conversion system. For example, when a power conversion systemhas an output level of 5V/1 A, a rectifying diode with a forward voltageof 0.3V-0.4V causes a power loss of about 0.3 W-0.4 W at a full load(e.g., 1 A). The reduction of the system efficiency is about 4%-6%.

In addition, in order for the power conversion system 200 to achieve lowstandby power consumption, the switching frequency is often kept low toreduce switching loss under no load or light load conditions. However,when the power conversion system 200 changes from no/light loadconditions to full load conditions, the output voltage 250 may dropabruptly and such a voltage drop may not be detected by the systemcontroller 202 instantly because the system controller 202 can oftendetect the output voltage only during a demagnetization process of eachswitching cycle. Therefore, the dynamic performance of the powerconversion system 200 is often unsatisfactory at a low switchingfrequency under no/light load conditions. For example, the powerconversion system 200 has an output level of 5V/1 A and the outputcapacitor 264 has a capacitance of 1000 μF. Under no/light loadconditions, the switching frequency is 1 kHz corresponding to aswitching period of 1 ms. If the output load changes from no/light loadconditions (e.g., 0 A) to full load conditions (e.g., 1 A), the outputvoltage 250 drops 1 V (e.g., from 5 V to 4 V), which is oftenunacceptable in certain applications.

Hence, it is highly desirable to improve techniques for rectificationand output detection of a power conversion system.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods with outputdetection and synchronized rectifying mechanisms. Merely by way ofexample, the invention has been applied to a power conversion system.But it would be recognized that the invention has a much broader rangeof applicability.

According to one embodiment, a system controller for regulating a powerconversion system includes a first controller terminal and a secondcontroller terminal. The system controller is configured to receive atleast an input signal at the first controller terminal, and generate agate drive signal at the second controller terminal based on at leastinformation associated with the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. The system controller is furtherconfigured to, if the input signal is larger than a first threshold,generate the gate drive signal at a first logic level to turn off thetransistor, and if the input signal changes from a first value largerthan a second threshold to a second value smaller than the secondthreshold, change the gate drive signal from the first logic level to asecond logic level to turn on the transistor.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal and asecond controller terminal. The system controller is configured toreceive at least an input signal at the first controller terminal, theinput signal being proportional to an output voltage associated with asecondary winding of the power conversion system, and generate a gatedrive signal at the second controller terminal based on at leastinformation associated with the input signal to turn on or off atransistor in order to affect a current associated with the secondarywinding of the power conversion system. The system controller is furtherconfigured to, only if the input signal changes from a first valuelarger than a first threshold to a second value smaller than the firstthreshold, generate a pulse of the gate drive signal to turn on thetransistor during a pulse period associated with the pulse.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first comparator, a signaldetector, and a driving component. The first comparator is configured toreceive an input signal and output a first comparison signal based on atleast information associated with the input signal. The signal detectoris configured to receive the input signal and output a first detectionsignal based on at least information associated with the input signal.The driving component is configured to output a gate drive signal basedon at least information associated with the first comparison signal andthe first detection signal to turn on or off a transistor in order toaffect a current associated with a secondary winding of the powerconversion system. The comparator is further configured to determinewhether the input signal is larger than a first threshold. The signaldetector is further configured to determine whether the input signalchanges from a first value larger than a second threshold to a secondvalue smaller than the second threshold. The driving component isfurther configured to, if the first comparison signal indicates theinput signal is larger than the first threshold, generate the gate drivesignal at a first logic level to turn off the transistor, and if thefirst detection signal indicates the input signal changes from the firstvalue larger than the second threshold to the second value smaller thanthe second threshold, change the gate drive signal from the first logiclevel to a second logic level to turn on the transistor.

In one embodiment, a system controller for regulating a power conversionsystem includes a comparator, a pulse signal generator, and a drivingcomponent. A comparator is configured to receive an input signal andoutput a comparison signal based on at least information associated withthe input signal. The pulse signal generator is configured to receive atleast the comparison signal and generate a pulse signal based on atleast information associated with the comparison signal. The drivingcomponent is configured to receive the pulse signal and generate a gatedrive signal based on at least information associated with the pulsesignal to turn on or off a transistor in order to affect a currentassociated with the secondary winding of the power conversion system.The comparator is further configured to determine whether the inputsignal is larger than or smaller than a threshold. The pulse signalgenerator is further configured to, only if the comparison signalindicates the input signal changes from a first value larger than thethreshold to a second value smaller than the threshold, generate a firstpulse of the pulse signal. The driving component is further configuredto, in response to the first pulse of the pulse signal, generate asecond pulse of the gate drive signal to turn on the transistor during apulse period associated with the second pulse.

In another embodiment, a method for regulating a power conversion systemincludes receiving at least an input signal, processing informationassociated with the input signal, and generating a gate drive signalbased on at least information associated with the input signal to turnon or off a transistor in order to affect a current associated with asecondary winding of the power conversion system. The process forgenerating a gate drive signal based on at least information associatedwith the input signal to turn on or off a transistor in order to affecta current associated with a secondary winding of the power conversionsystem includes, if the input signal is larger than a first threshold,generating the gate drive signal at a first logic level to turn off thetransistor, and if the input signal changes from a first value largerthan a second threshold to a second value smaller than the secondthreshold, changing the gate drive signal from the first logic level toa second logic level to turn on the transistor.

In yet another embodiment, a method for regulating a power conversionsystem includes receiving at least an input signal, the input signalbeing proportional to an output voltage associated with a secondarywinding of the power conversion system, processing informationassociated with the input signal, and generating a gate drive signalbased on at least information associated with the input signal to turnon or off a transistor in order to affect a current associated with thesecondary winding of the power conversion system. The process forgenerating a gate drive signal based on at least information associatedwith the input signal to turn on or off a transistor in order to affecta current associated with the secondary winding of the power conversionsystem includes, only if the input signal changes from a first valuelarger than a first threshold to a second value smaller than the firstthreshold, generating a pulse of the gate drive signal to turn on thetransistor during a pulse period associated with the pulse.

In yet another embodiment, a method for regulating a power conversionsystem includes receiving an input signal, processing informationassociated with the input signal, and determining whether the inputsignal is larger than a first threshold. The method further includesgenerating a comparison signal based on at least information associatedwith the input signal, determining whether the input signal changes froma first value larger than a second threshold to a second value smallerthan the second threshold, and generating a detection signal based on atleast information associated with the input signal. In addition, themethod includes outputting a gate drive signal based on at leastinformation associated with the comparison signal and the detectionsignal to turn on or off a transistor in order to affect a currentassociated with a secondary winding of the power conversion system. Theprocess for outputting a gate drive signal based on at least informationassociated with the comparison signal and the detection signal to turnon or off a transistor in order to affect a current associated with asecondary winding of the power conversion system includes, if thecomparison signal indicates the input signal is larger than the firstthreshold, generating the gate drive signal at a first logic level toturn off the transistor, and if the detection signal indicates the inputsignal changes from the first value larger than the second threshold tothe second value smaller than the second threshold, changing the gatedrive signal from the first logic level to a second logic level to turnon the transistor.

In yet another embodiment, a method for regulating a power conversionsystem includes receiving an input signal, processing informationassociated with the input signal, and determining whether the inputsignal is larger than or smaller than a threshold. The method furtherincludes generating a comparison signal based on at least informationassociated with the first input signal, receiving the comparison signal,and processing information associated with the comparison signal. Inaddition, the method includes generating a pulse signal based on atleast information associated with the comparison signal, receiving thepulse signal, processing information associated with the pulse signal,and generating a gate drive signal based on at least informationassociated with the pulse signal to turn on or off a transistor in orderto affect a current associated with the secondary winding of the powerconversion system. The process for generating a pulse signal based on atleast information associated with the comparison signal includes, onlyif the comparison signal indicates the input signal changes from a firstvalue larger than the threshold to a second value smaller than thethreshold, generating a first pulse of the pulse signal. The process forgenerating a gate drive signal based on at least information associatedwith the pulse signal to turn on or off a transistor in order to affecta current associated with the secondary winding of the power conversionsystem includes, in response to the first pulse of the pulse signal,generate a second pulse of the gate drive signal to turn on thetransistor during a pulse period associated with the second pulse.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether the input signal is larger than a firstthreshold at a first time, in response to the input signal beingdetermined to be larger than the first threshold at the first time,determine whether the input signal is smaller than a second threshold ata second time, and in response to the input signal being determined tobe smaller than the second threshold at the second time, change thedrive signal at the second controller terminal from a first logic levelto a second logic level. Also, the second time is after the first time.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether the input signal remains larger than afirst threshold for a time period that is longer than a predeterminedduration, and in response to the input signal being determined to haveremained larger than the first threshold for the time period that islonger than the predetermined duration, determine whether the inputsignal is smaller than a second threshold at a time following the timeperiod. Moreover, the system controller is further configured to, inresponse to the input signal being determined to be smaller than thesecond threshold at the time, change the drive signal at the secondcontroller terminal from a first logic level to a second logic level.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal, and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether a time interval from a first time whenthe input signal becomes larger than a first threshold to a second timewhen the input signal becomes smaller than a second threshold is longerthan a predetermined duration, and in response to the time intervalbeing determined to be longer than the predetermined duration, determinewhether the input signal is smaller than a third threshold at a timefollowing the time interval. Also, the system controller is furtherconfigured to, in response to the input signal being determined to besmaller than the third threshold at the time, change the drive signal atthe second controller terminal from a first logic level to a secondlogic level.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether the input signal is larger than a firstthreshold, determine whether the input signal remains larger than asecond threshold for a time period that is longer than a firstpredetermined duration, and determine whether a time interval from afirst time when the input signal becomes larger than a third thresholdto a second time when the input signal becomes smaller than a fourththreshold is longer than a second predetermined duration. Also, thesystem controller is further configured to, in response to the inputsignal being determined to be larger than the first threshold, the inputsignal being determined to be larger than the second threshold for thetime period that is longer than the first predetermined duration, or thetime interval being determined to be longer than the secondpredetermined duration, determine whether the input signal is smallerthan a fifth threshold, and in response to the input signal beingdetermined to be smaller than the fifth threshold, change the drivesignal at the second controller terminal from a first logic level to asecond logic level.

According to yet another embodiment, a method for regulating a powerconversion system includes receiving an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether the input signal is larger than a first threshold at a firsttime. Moreover, the generating a drive signal based at least in part onthe input signal to turn on or off a transistor in order to affect acurrent associated with a secondary winding of the power conversionsystem includes, in response to the input signal being determined to belarger than the first threshold at the first time, determining whetherthe input signal is smaller than a second threshold at a second time,and in response to the input signal being determined to be smaller thanthe second threshold at the second time, changing the drive signal froma first logic level to a second logic level. Also, the second time isafter the first time.

According to yet another embodiment, a method for regulating a powerconversion system includes receiving an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether the input signal remains larger than a first threshold for atime period that is longer than a predetermined duration. Moreover, thegenerating a drive signal based at least in part on the input signal toturn on or off a transistor in order to affect a current associated witha secondary winding of the power conversion system includes, in responseto the input signal being determined to have remained larger than thefirst threshold for the time period that is longer than thepredetermined duration, determining whether the input signal is smallerthan a second threshold at a time following the time period, and inresponse to the input signal being determined to be smaller than thesecond threshold at the time, changing the drive signal from a firstlogic level to a second logic level.

According to yet another embodiment, a method for regulating a powerconversion system includes receiving an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether a time interval from a first time when the input signal becomeslarger than a first threshold to a second time when the input signalbecomes smaller than a second threshold is longer than a predeterminedduration. Moreover, the generating a drive signal based at least in parton the input signal to turn on or off a transistor in order to affect acurrent associated with a secondary winding of the power conversionsystem includes, in response to the time interval being determined to belonger than the predetermined duration, determining whether the inputsignal is smaller than a third threshold at a time following the timeinterval, and in response to the input signal being determined to besmaller than the third threshold at the time, change the drive signalfrom a first logic level to a second logic level.

According to yet another embodiment, a method for regulating a powerconversion system includes receive an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether the input signal is larger than a first threshold, determiningwhether the input signal remains larger than a second threshold for atime period that is longer than a first predetermined duration, anddetermining whether a time interval from a first time when the inputsignal becomes larger than a third threshold to a second time when theinput signal becomes smaller than a fourth threshold is longer than asecond predetermined duration. Moreover, the generating a drive signalbased at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system includes, in response to theinput signal being determined to be larger than the first threshold, theinput signal being determined to be larger than the second threshold forthe time period that is longer than the first predetermined duration, orthe time interval being determined to be longer than the secondpredetermined duration, determining whether the input signal is smallerthan a fifth threshold, and in response to the input signal beingdetermined to be smaller than the fifth threshold, changing the drivesignal from a first logic level to a second logic level.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional flyback powerconversion system.

FIG. 2(A) is a simplified diagram showing another conventional flybackpower conversion system.

FIG. 2(B) is a simplified conventional timing diagram for the flybackpower conversion system as shown in FIG. 2(A) that operates in thediscontinuous conduction mode (DCM).

FIG. 3(A) is a simplified diagram showing a power conversion system witha rectifying circuit according to an embodiment of the presentinvention.

FIG. 3(B) is a simplified diagram showing a power conversion system witha rectifying circuit according to another embodiment of the presentinvention.

FIG. 4 is a simplified timing diagram for the power conversion system asshown in FIG. 3(A) operating in the discontinuous conduction mode (DCM)according to an embodiment of the present invention.

FIG. 5 is a simplified diagram showing certain components of thesecondary controller as part of the power conversion system as shown inFIG. 3(A) according to an embodiment of the present invention.

FIG. 6 is a simplified timing diagram for the power conversion system asshown in FIG. 3(A) that includes the secondary controller as shown inFIG. 5 and operates in the discontinuous conduction mode (DCM) accordingto an embodiment of the present invention.

FIG. 7 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to another embodiment of the present invention.

FIG. 8 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to yet another embodiment of the present invention.

FIG. 9 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to yet another embodiment of the present invention.

FIG. 10 is a simplified diagram showing certain components of thesecondary controller 308 as part of the power conversion system 300according to another embodiment of the present invention.

FIG. 11 is a simplified diagram showing a method for enabling thefalling-edge detection component 1110 of the secondary controller 308 aspart of the power conversion system 300 according to one embodiment ofthe present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods with outputdetection and synchronized rectifying mechanisms. Merely by way ofexample, the invention has been applied to a power conversion system.But it would be recognized that the invention has a much broader rangeof applicability.

FIG. 3(A) is a simplified diagram showing a power conversion system witha rectifying circuit according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The powerconversion system 300 includes a controller 302, a primary winding 304,a secondary winding 306, an auxiliary winding 324, a rectifying circuit301, a diode 320, a current sensing resistor 328, capacitors 312 and380, resistors 314, 316, 322 and 326, and a power switch 330. Therectifying circuit 301 includes a secondary controller 308, a resistor318 and a transistor 310. The secondary controller 308 includesterminals 390, 392, 394, 396 and 398. For example, the transistor 310 isa MOSFET. In another example, the power switch 330 is a transistor.

According to one embodiment, when the power switch 330 is closed (e.g.,on), the energy is stored in the transformer that includes the primarywinding 304 and the secondary winding 306. For example, when the powerswitch 330 is open (e.g., off), the stored energy is transferred to thesecondary side, and the voltage of the auxiliary winding 324 maps anoutput voltage 350 on the secondary side. In another example, thecontroller 302 receives a feedback signal 360 from a voltage dividerthat includes the resistors 322 and 326 for output voltage regulation.In yet another example, during the process of energy transfer (e.g., ademagnetization process), the transistor 310 is turned on and at leastpart of a secondary current 352 flows through the transistor 310. In yetanother example, a turn-on resistance of the transistor 310 is verysmall (e.g., in the range of tens of milli-ohms). In yet anotherexample, the voltage drop on the transistor 310 when conducting is muchsmaller than a voltage drop on a rectifying diode (e.g., the diode 124or the diode 260), and thus the power loss of the power conversionsystem 300 is greatly reduced compared with the system 100 or the system200.

According to another embodiment, at the end of the energy transferprocess (e.g., the demagnetization process), the secondary current 352has a low value (e.g., nearly zero). For example, the transistor 310 isturned off to prevent a residual current flowing from an output terminal351 to ground through the transistor 310. In another example, the powerswitch 330 remains off (e.g., open) when the transistor 310 is on. Inyet another example, the secondary controller 308 receives a voltagesignal 362 (e.g., V_(DR)) indicative of a voltage at a terminal 364 ofthe transistor 310 (e.g., a drain terminal of the transistor 310), andprovides a signal 366 (e.g., at terminal G2) to drive the transistor310.

As discussed above and further emphasized here, FIG. 3(A) is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the controller 302 and the secondarycontroller 308 are on different chips. In another example, the secondarycontroller 308 and the transistor 310 are on different chips which areparts of a multi-chip package. In yet another example, the secondarycontroller 308 and the transistor 310 are integrated on a same chip.

FIG. 3(B) is a simplified diagram showing a power conversion system witha rectifying circuit according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The powerconversion system 400 includes a controller 402, a primary winding 404,a secondary winding 406, a first auxiliary winding 424, a secondauxiliary winding 425, a rectifying circuit 401, diodes 420 and 474,capacitors 412, 476 and 478, a current sensing resistor 428, resistors414, 416, 470 and 472, and a power switch 430. The rectifying circuit401 includes a secondary controller 408, a resistor 418 and a transistor410. For example, the transistor 410 is a MOSFET. In another example,the power switch 430 is a transistor. In yet another example, therectifying circuit 401 is the same as the rectifying circuit 301.

According to one embodiment, when the power switch 430 is closed (e.g.,on), the energy is stored in the transformer that includes the primarywinding 404 and the secondary winding 406. For example, when the powerswitch 430 is open (e.g., off), the stored energy is transferred to thesecondary side, and the voltage of the second auxiliary winding 425 mapsan output voltage 450 on the secondary side. In another example, thecontroller 402 receives a feedback signal 460 from a voltage dividerthat includes the resistors 470 and 472 for output voltage regulation.In another example, during the process of energy transfer (e.g., ademagnetization process), the transistor 410 is turned on and at leastpart of a secondary current 452 flows through the transistor 410. In yetanother example, a turn-on resistance of the transistor 410 is verysmall (e.g., in the range of tens of milli-ohms).

According to another embodiment, at the end of the energy transferprocess (e.g., the demagnetization process), the secondary current 452has a low value (e.g., nearly zero). For example, the transistor 410 isturned off to prevent a reversal current from flowing from an outputterminal to ground through the transistor 410. In another example, thepower switch 430 remains off (e.g., open) when the transistor 410 is on.In yet another example, the secondary controller 408 receives (e.g., atterminal DR) a voltage signal 462 indicative of a voltage at a terminal464 of the transistor 410 (e.g., a drain terminal of the transistor410), and provides a signal 466 (e.g., at terminal G2) to drive thetransistor 410.

As discussed above and further emphasized here, FIG. 3(B) is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the controller 402 and the secondarycontroller 408 are on different chips. In another example, the secondarycontroller 408 and the transistor 410 are on different chips which arepart of a multi-chip package. In yet another example, the secondarycontroller 408 and the transistor 410 are integrated on a same chip.

FIG. 4 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to an embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the waveform502 represents the power switch 330 being turned on or off as a functionof time, the waveform 504 represents the secondary current 352 as afunction of time, and the waveform 506 represents the feedback signal360 as a function of time. In addition, the waveform 508 represents thevoltage signal 362 (e.g., at terminal DR) as a function of time, thewaveform 510 represents the signal 366 (e.g., at terminal G2) as afunction of time, the waveform 512 represents a channel current 368 thatflows through the transistor 310 as a function of time, and the waveform514 represents a body-diode current 370 that flows through a body diodeof the transistor 310 (e.g., a parasitic diode) as a function of time.

For example, a switching period of the switch 330 includes an on-timeperiod during which the switch 330 is closed (e.g., on) and an off-timeperiod during which the switch 330 is open (e.g., off). In anotherexample, as shown in FIG. 4 , an on-time period of the switch 330 (e.g.,T_(on)) starts at time t₄ and ends at time t₅, and an off-time period ofthe switch 330 (e.g., T_(off)) starts at the time t₅ and ends at timet₉. A demagnetization period associated with the transformer includingthe primary winding 304 and the secondary winding 306 (e.g., T_(demag))starts at the time t₅ and ends at time t₈. In yet another example,t₄≤t₅≤t₆≤t₇≤t₈≤t₉.

According to one embodiment, during the on-time period (e.g., T_(on)),the switch 330 is closed (e.g., being turned on) as shown by thewaveform 502, and the energy is stored in the transformer that includesthe primary winding 304 and the secondary winding 306. For example, thesecondary current 352 has a low value 516 (e.g., nearly zero) as shownby the waveform 504. In another example, the voltage signal 362 (e.g.,V_(DR)) received by the secondary controller 308 has a value 518 whichis higher than zero (e.g., as shown by the waveform 508). In yet anotherexample, the signal 366 is at a logic low level (e.g., as shown by thewaveform 510), and the transistor 310 is off. In yet another example,during the on-time period (e.g., T_(on)), the channel current 368 has alow value 520 (e.g., nearly zero as shown by the waveform 512) and thebody-diode current 370 has a low value 522 (e.g., nearly zero as shownby the waveform 514).

According to another embodiment, at the end of the on-time period (e.g.,at t₅), the switch 330 is open (e.g., off) as shown by the waveform 502,and the energy is transferred to the secondary side. For example, thesecondary current 352 increases from the value 516 to a value 524 (e.g.,at t₅) as shown by the waveform 504. In another example, the voltagesignal 362 (e.g., V_(DR)) decreases from the value 518 to a value 526(e.g., as shown by the waveform 508). In yet another example, the value526 is lower than both a first threshold voltage 528 (e.g., V_(th1)) anda second threshold voltage 530 (e.g., V_(th2)). In yet another example,both the first threshold voltage 528 (e.g., V_(th1)) and the secondthreshold voltage 530 (e.g., V_(th2)) are lower than a ground voltage372 (e.g., zero volt). In yet another example, the body diode of thetransistor 310 begins to conduct, and the body-diode current 370increases from the value 522 to a value 529 (e.g., as shown by thewaveform 514). Thereafter, the signal 366 changes from the logic lowlevel to a logic high level (e.g., at t₆ as shown by the waveform 510)and the transistor 310 is turned on in certain embodiments. For example,the channel current 368 increases from the value 520 to a value 525(e.g., at t₆ as shown by the waveform 512). In another example, there isa delay (e.g., T_(d)) between the time at which the voltage signal 362(e.g., V_(DR)) decreases from the value 518 to a value 526 and the timeat which the signal 366 changes from the logic low level to the logichigh level. In yet another example, the delay (e.g., T_(d)) is zero.

According to yet another embodiment, during the demagnetization period(e.g., T_(demag)), the switch 330 remains open (e.g., off) as shown bythe waveform 502. For example, the secondary current 352 decreases fromthe value 524 as shown by the waveform 504. In another example, if thevoltage signal 362 (e.g., V_(DR)) is larger than the first thresholdvoltage 528 (e.g., at t₇ as shown by the waveform 508), the signal 366changes from the logic high level to the logic low level (e.g., as shownby the waveform 510). In yet another example, the voltage signal 362(e.g., V_(DR)) decreases to become lower than the first thresholdvoltage 528 again (e.g., at t₈ as shown by the waveform 508). In yetanother example, the transistor 310 is turned off, and the channelcurrent 368 decreases to a low value 534 (e.g., nearly zero as shown bythe waveform 512). In yet another example, the body-diode current 370flows through the body diode of the transistor 310, and decreases to alow value (e.g., nearly zero at t₉ as shown by the waveform 514). In yetanother example, the demagnetization period ends at the time t₉. In yetanother example, immediately after the time t₉, the voltage signal 362increases as shown by a rising edge in the waveform 508, and such arising edge, even if detected, is not used for determining the switchingfrequency of the power conversion system 300 (e.g., the loadconditions). In yet another example, the secondary current 352 is equalto a sum of the channel current 368 and the body-diode current 370.Thus, a combination of part of the waveform 512 (e.g., between t₅ andt₉) and part of the waveform 514 (e.g., between t₅ and t₉) is equal topart of the waveform 504 (e.g., between t₅ and t₉) in certainembodiments.

According to yet another embodiment of the present invention, FIG. 4 isa simplified timing diagram for the power conversion system 400 shown inFIG. 3(B) operating in the discontinuous conduction mode (DCM). Forexample, the waveform 502 represents the power switch 430 being turnedon or off as a function of time, the waveform 504 represents thesecondary current 452 as a function of time, and the waveform 506represents the feedback signal 460 as a function of time. In addition,the waveform 508 represents the voltage signal 462 (e.g., at terminalDR) as a function of time, the waveform 510 represents the signal 466(e.g., at terminal G2) as a function of time, the waveform 512represents a channel current 468 that flows through the transistor 410as a function of time, and the waveform 514 represents a body-diodecurrent 480 that flows through a body diode of the transistor 410 (e.g.,a parasitic diode) as a function of time.

As discussed above and further emphasized here, FIG. 4 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the power conversion system 300 shown inFIG. 3(A) or the power conversion system 400 shown in FIG. 3(B)operating in other modes, such as a continuous conduction mode and thecritical conduction mode (e.g., the quasi-resonant mode), can alsoimplement the scheme as illustrated in FIG. 4 .

In certain embodiments, the scheme as illustrated in FIG. 4 isimplemented in the continuous conduction mode. For example, if thesecondary controller 308 detects a falling edge of the signal 362 (e.g.,V_(DR)), the secondary controller 308 changes the signal 366 to turn onthe transistor 310. In another example, the controller 302 turns on thetransistor 330 before the demagnetization period ends (e.g., thesecondary current 352 being larger than zero), and in response thesignal 362 (e.g., V_(DR)) increases. In yet another example, thesecondary controller 308 detects a rising edge of the signal 362 andchanges the signal 366 to turn off the transistor 310.

FIG. 5 is a simplified diagram showing certain components of thesecondary controller 308 as part of the power conversion system 300according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The secondary controller308 includes a clamping component 602, an offset component 604, arising-edge detection component 606, comparators 608 and 624, afalling-edge detection component 610, a timing controller 612, a logiccontrol component 614, a gate driver 616, a light-load detector 618, asignal generator 620, an oscillator 622, an under-voltage-lockoutcomponent 628, and a reference-signal generator 626. For example, somecomponents of the secondary controller 308 are used for synchronizedrectifying, including the clamping component 602, the offset component604, the rising-edge detection component 606, the comparator 608, thefalling-edge detection component 610, the timing controller 612, thelogic control component 614, and the gate driver 616. In anotherexample, certain components of the secondary controller 308 are used foroutput voltage detection and control, including the light-load detector618, the signal generator 620, the oscillator 622, the reference-signalgenerator 626, the logic control component 614, and the gate driver 616.In yet another example, the components of the secondary controller 308that are used for synchronized rectifying and the components of thesecondary controller 308 that are used for output voltage detection andcontrol are integrated on a same chip.

FIG. 6 is a simplified timing diagram for the power conversion system300 that includes the secondary controller 308 as shown in FIG. 5 andoperates in the discontinuous conduction mode (DCM) according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. For example, the waveform 702 represents the power switch330 being turned on or off as a function of time, the waveform 704represents the feedback signal 360 as a function of time, and thewaveform 706 represents the voltage signal 362 (e.g., at terminal 390)as a function of time. In addition, the waveform 708 represents thesignal 366 (e.g., at terminal 392) as a function of time, the waveform710 represents a channel current 368 that flows through the transistor310 as a function of time, and the waveform 712 represents a voltagesignal 388 (e.g., at terminal 398) that indicates the output voltage 350as a function of time.

According to one embodiment, the clamping component 602 receives thevoltage signal 362 (e.g., V_(DR)) from the terminal 390 (e.g., terminalDR). For example, the rising-edge detection component 606, thecomparator 608 and the falling edge detection component 610 receive asignal 658 which is equal to the voltage signal 362 modified by theoffset component 604. In another example, the rising-edge detectioncomponent 606, the comparator 608 and the falling edge detectioncomponent 610 output signals 670, 660 and 650 respectively based on atleast information associated with the signal 658. In yet anotherexample, the timing controller 612 receives the signals 670, 660 and 650and outputs a signal 672 to the logic controller 614 in order to drivethe transistor 310. The offset component 604 is omitted in someembodiments.

According to another embodiment, before time t₁₆, the power conversionsystem 300 is under no/light load conditions and the switching frequencyof the system 300 is kept low (e.g., lower than a threshold). Forexample, during an on-time period (e.g., between time t₁₁ and time t₁₂),the switch 330 is closed (e.g., being turned on) as shown by thewaveform 702, and the energy is stored in the transformer that includesthe primary winding 304 and the secondary winding 306. In anotherexample, the voltage signal 362 (e.g., at terminal DR) has a value 714(e.g., as shown by the waveform 706), and is clamped by the clampingcomponent 602. In yet another example, the signal 366 (e.g., at terminalG2) is at a logic low level (e.g., as shown by the waveform 708), andthe transistor 310 is off. In yet another example, during the on-timeperiod (e.g., T_(on)), the channel current 368 has a low value 716(e.g., nearly zero as shown by the waveform 710). In yet anotherexample, the voltage signal 388 (e.g., V_(s)) has a value 718 (e.g., asshown by the waveform 712).

According to yet another embodiment, at the end of the on-time period(e.g., at t₁₂), the switch 330 is open (e.g., off) as shown by thewaveform 702, and the energy is transferred to the secondary side. Forexample, the voltage signal 362 decreases from the value 714 to a value720 (e.g., as shown by the waveform 706). In yet another example, thevalue 720 is lower than both a third threshold voltage 722 (e.g.,V_(th3)) and a fourth threshold voltage 724 (e.g., V_(th4)). In yetanother example, both the third threshold voltage 722 (e.g., V_(th3))and the fourth threshold voltage 724 (e.g., V_(th4)) are lower than aground voltage 372. In yet another example, the body diode of thetransistor 310 begins to conduct, and the body-diode current 370increases in magnitude. Thereafter, the signal 366 changes from thelogic low level to a logic high level (e.g., at t₁₃ as shown by thewaveform 708), and the transistor 310 is turned on in certainembodiments. For example, the third threshold voltage 722 (e.g.,V_(th3)) and the fourth threshold voltage 724 (e.g., V_(th4)) are thesame as the first threshold voltage 528 and the second threshold voltage530, respectively.

According to yet another embodiment, when the voltage signal 362decreases from the value 714 to the value 720 (e.g., as shown by thewaveform 706), the falling-edge detection component 610 detects the dropof the voltage signal 362 and changes the signal 650 in order to turn onthe transistor 310. For example, in response, the channel current 368increases from the value 716 to a value 726 (e.g., at t₁₃ as shown bythe waveform 710). In another example, a voltage drop between the drainterminal and the source terminal of the transistor 310 is determinedbased on the following equation:V _(DS_M2) =−I _(sec) ×R _(ds_on)  (Equation 1)where V_(DS_M2) represents the voltage drop between the drain terminaland the source terminal of the transistor 310, I_(sec) represents thesecondary current 352, and R_(ds_on) represents a turn-on resistance ofthe transistor 310.

Because the turn-on resistance of the transistor 310 is very small, themagnitude of the voltage drop between the drain terminal and the sourceterminal of the transistor 310 is much smaller than a forward voltage ofa rectifying diode (e.g., the diode 124 or the diode 260), according tocertain embodiments. For example, when the secondary current 352 becomesvery small (e.g., approximately zero), the voltage drop between thedrain terminal and the source terminal of the transistor 310 becomesvery small in magnitude, and the voltage signal 362 is very small inmagnitude. In another example, if the signal 658 is larger than thereference signal 652 in magnitude, the comparator 608 changes the signal660 in order to turn off the transistor 310. In yet another example, thesignal 366 changes from the logic high level to the logic low level(e.g., at t₁₄ as shown by the waveform 708) and the transistor 310 isturned off. In yet another example, the body diode of the transistor 310begins to conduct again, and the body-diode current 370 decreases inmagnitude (e.g., eventually to nearly zero at t₁₅). Thus, the energy iscompletely delivered to the output in some embodiments.

In one embodiment, the secondary controller 308 continuously monitorsthe output voltage 350 through the signal 388 (e.g., V_(s)). Forexample, the comparator 624 receives a reference signal 680 and thesignal 388 (e.g., V_(s)) and outputs a signal 682. In another example,the light-load detector 618 receives a clock signal from the oscillator622 and a signal 676 from the timing controller 612. In yet anotherexample, the signal 676 indicates certain switching events (e.g., risingedges or falling edges) in the signal 362. In yet another example, thelight-load detector 618 outputs a signal 678 which indicates theswitching frequency of the power conversion system 300. In yet anotherexample, the signal generator 620 receives the signal 678 and the signal682 and outputs a signal 684 to the logic control component 614 in orderto affect the status of the transistor 310.

In another embodiment, if the output voltage 350 drops below a thresholdlevel in any conditions, for example, when the output load conditionschanges from no/light load conditions to full load conditions (e.g.,between t₁₆ and t₁₇), the output voltage 350 decreases (e.g., below athreshold level). For example, if the signal 388 (e.g., V_(s)) changesfrom a first value larger than the reference signal 680 in magnitude toa second value lower than the reference signal 680 in magnitude (e.g.,at t₁₆ as shown by the waveform 712), the comparator 624 generates apulse in the signal 682 in order to turn on the transistor 310 during ashort time period. In some embodiments, if the signal 678 indicates thatthe power conversion system 300 is under no/light load conditions, thesignal generator 620 outputs a pulse in the signal 684, and in responsethe gate driver 616 generates a pulse 730 in the signal 366 (e.g., asshown by the waveform 708). For example, the signal 362 (e.g., atterminal DR) decreases to a value 728 (e.g., between t₁₆ and t₁₇ asshown by the waveform 706). In yet another example, the transistor 310is turned on during a pulse period associated with the pulse 730 in thesignal 366, and the channel current 368 flows in a different direction(e.g., from the output capacitor 312 through the transistor 310 toground) as shown by the waveform 710. In yet another example, thefeedback signal 360 increases in magnitude, and forms a pulse (e.g.,between t₁₆ and t₁₇ as shown by the waveform 704). The controller 302detects the pulse of the feedback signal 360 and, in response, increasesthe peak current of the primary winding 304 and the switching frequencyin order to deliver more energy to the secondary side according tocertain embodiments. For example, the output voltage 350 and the voltagesignal 388 increase in magnitude eventually (e.g., at t₁₈ as shown bythe waveform 712).

As discussed above and further emphasized here, FIG. 5 and FIG. 6 aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, the secondary controller408 is the same as the secondary controller 308 as shown in FIG. 5 .

In certain embodiments, FIG. 6 is a simplified timing diagram for thepower conversion system 400 that includes the secondary controller 408and operates in the discontinuous conduction mode (DCM). For example,the waveform 702 represents the power switch 430 being turned on or offas a function of time, the waveform 704 represents the feedback signal460 as a function of time, and the waveform 706 represents the voltagesignal 462 as a function of time. In addition, the waveform 708represents the signal 466 as a function of time, the waveform 710represents a channel current 468 that flows through the transistor 410as a function of time, and the waveform 712 represents a voltage signal488 that indicates the output voltage 450 as a function of time.

In some embodiments, the secondary controller 308 as part of the powerconversion system 300 or the secondary controller 408 as part of thepower conversion system 400 operating in other modes, such as acontinuous conduction mode and the critical conduction mode (e.g., thequasi-resonant mode), can also implement the scheme as illustrated inFIG. 5 and FIG. 6 .

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal and asecond controller terminal. The system controller is configured toreceive at least an input signal at the first controller terminal, andgenerate a gate drive signal at the second controller terminal based onat least information associated with the input signal to turn on or offa transistor in order to affect a current associated with a secondarywinding of the power conversion system. The system controller is furtherconfigured to, if the input signal is larger than a first threshold,generate the gate drive signal at a first logic level to turn off thetransistor, and if the input signal changes from a first value largerthan a second threshold to a second value smaller than the secondthreshold, change the gate drive signal from the first logic level to asecond logic level to turn on the transistor. For example, the system isimplemented according to FIG. 3(A), FIG. 3(B), FIG. 4 , FIG. 5 , and/orFIG. 6 .

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal and asecond controller terminal. The system controller is configured toreceive at least an input signal at the first controller terminal, theinput signal being proportional to an output voltage associated with asecondary winding of the power conversion system, and generate a gatedrive signal at the second controller terminal based on at leastinformation associated with the input signal to turn on or off atransistor in order to affect a current associated with the secondarywinding of the power conversion system. The system controller is furtherconfigured to, only if the input signal changes from a first valuelarger than a first threshold to a second value smaller than the firstthreshold, generate a pulse of the gate drive signal to turn on thetransistor during a pulse period associated with the pulse. For example,the system is implemented according to at least FIG. 3(A), FIG. 3(B),FIG. 5 , and/or FIG. 6 .

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first comparator, a signaldetector, and a driving component. The first comparator is configured toreceive an input signal and output a first comparison signal based on atleast information associated with the input signal. The signal detectoris configured to receive the input signal and output a first detectionsignal based on at least information associated with the input signal.The driving component is configured to output a gate drive signal basedon at least information associated with the first comparison signal andthe first detection signal to turn on or off a transistor in order toaffect a current associated with a secondary winding of the powerconversion system. The comparator is further configured to determinewhether the input signal is larger than a first threshold. The signaldetector is further configured to determine whether the input signalchanges from a first value larger than a second threshold to a secondvalue smaller than the second threshold. The driving component isfurther configured to, if the first comparison signal indicates theinput signal is larger than the first threshold, generate the gate drivesignal at a first logic level to turn off the transistor, and if thefirst detection signal indicates the input signal changes from the firstvalue larger than the second threshold to the second value smaller thanthe second threshold, change the gate drive signal from the first logiclevel to a second logic level to turn on the transistor. For example,the system is implemented according to FIG. 3(A), FIG. 3(B), FIG. 4 ,FIG. 5 , and/or FIG. 6 .

In one embodiment, a system controller for regulating a power conversionsystem includes a comparator, a pulse signal generator, and a drivingcomponent. A comparator is configured to receive an input signal andoutput a comparison signal based on at least information associated withthe input signal. The pulse signal generator is configured to receive atleast the comparison signal and generate a pulse signal based on atleast information associated with the comparison signal. The drivingcomponent is configured to receive the pulse signal and generate a gatedrive signal based on at least information associated with the pulsesignal to turn on or off a transistor in order to affect a currentassociated with the secondary winding of the power conversion system.The comparator is further configured to determine whether the inputsignal is larger than or smaller than a threshold. The pulse signalgenerator is further configured to, only if the comparison signalindicates the input signal changes from a first value larger than thethreshold to a second value smaller than the threshold, generate a firstpulse of the pulse signal. The driving component is further configuredto, in response to the first pulse of the pulse signal, generate asecond pulse of the gate drive signal to turn on the transistor during apulse period associated with the second pulse. For example, the systemis implemented according to at least FIG. 3(A), FIG. 3(B), FIG. 5 ,and/or FIG. 6 .

In another embodiment, a method for regulating a power conversion systemincludes receiving at least an input signal, processing informationassociated with the input signal, and generating a gate drive signalbased on at least information associated with the input signal to turnon or off a transistor in order to affect a current associated with asecondary winding of the power conversion system. The process forgenerating a gate drive signal based on at least information associatedwith the input signal to turn on or off a transistor in order to affecta current associated with a secondary winding of the power conversionsystem includes, if the input signal is larger than a first threshold,generating the gate drive signal at a first logic level to turn off thetransistor, and if the input signal changes from a first value largerthan a second threshold to a second value smaller than the secondthreshold, changing the gate drive signal from the first logic level toa second logic level to turn on the transistor. For example, the methodis implemented according to FIG. 3(A), FIG. 3(B), FIG. 4 , FIG. 5 ,and/or FIG. 6 .

In yet another embodiment, a method for regulating a power conversionsystem includes receiving at least an input signal, the input signalbeing proportional to an output voltage associated with a secondarywinding of the power conversion system, processing informationassociated with the input signal, and generating a gate drive signalbased on at least information associated with the input signal to turnon or off a transistor in order to affect a current associated with thesecondary winding of the power conversion system. The process forgenerating a gate drive signal based on at least information associatedwith the input signal to turn on or off a transistor in order to affecta current associated with the secondary winding of the power conversionsystem includes, only if the input signal changes from a first valuelarger than a first threshold to a second value smaller than the firstthreshold, generating a pulse of the gate drive signal to turn on thetransistor during a pulse period associated with the pulse. For example,the method is implemented according to at least FIG. 3(A), FIG. 3(B),FIG. 5 , and/or FIG. 6 .

In yet another embodiment, a method for regulating a power conversionsystem includes receiving an input signal, processing informationassociated with the input signal, and determining whether the inputsignal is larger than a first threshold. The method further includesgenerating a comparison signal based on at least information associatedwith the input signal, determining whether the input signal changes froma first value larger than a second threshold to a second value smallerthan the second threshold, and generating a detection signal based on atleast information associated with the input signal. In addition, themethod includes outputting a gate drive signal based on at leastinformation associated with the comparison signal and the detectionsignal to turn on or off a transistor in order to affect a currentassociated with a secondary winding of the power conversion system. Theprocess for outputting a gate drive signal based on at least informationassociated with the comparison signal and the detection signal to turnon or off a transistor in order to affect a current associated with asecondary winding of the power conversion system includes, if thecomparison signal indicates the input signal is larger than the firstthreshold, generating the gate drive signal at a first logic level toturn off the transistor, and if the detection signal indicates the inputsignal changes from the first value larger than the second threshold tothe second value smaller than the second threshold, changing the gatedrive signal from the first logic level to a second logic level to turnon the transistor. For example, the method is implemented according toFIG. 3(A), FIG. 3(B), FIG. 4 , FIG. 5 , and/or FIG. 6 .

In yet another embodiment, a method for regulating a power conversionsystem includes receiving an input signal, processing informationassociated with the input signal, and determining whether the inputsignal is larger than or smaller than a threshold. The method furtherincludes generating a comparison signal based on at least informationassociated with the first input signal, receiving the comparison signal,and processing information associated with the comparison signal. Inaddition, the method includes generating a pulse signal based on atleast information associated with the comparison signal, receiving thepulse signal, processing information associated with the pulse signal,and generating a gate drive signal based on at least informationassociated with the pulse signal to turn on or off a transistor in orderto affect a current associated with the secondary winding of the powerconversion system. The process for generating a pulse signal based on atleast information associated with the comparison signal includes, onlyif the comparison signal indicates the input signal changes from a firstvalue larger than the threshold to a second value smaller than thethreshold, generating a first pulse of the pulse signal. The process forgenerating a gate drive signal based on at least information associatedwith the pulse signal to turn on or off a transistor in order to affecta current associated with the secondary winding of the power conversionsystem includes, in response to the first pulse of the pulse signal,generate a second pulse of the gate drive signal to turn on thetransistor during a pulse period associated with the second pulse. Forexample, the method is implemented according to at least FIG. 3(A), FIG.3(B), FIG. 5 , and/or FIG. 6 .

FIG. 7 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the waveform802 represents the power switch 330 being turned on or off as a functionof time, the waveform 808 represents the voltage signal 362 (e.g.,V_(DR) at terminal DR) as a function of time, and the waveform 810represents the signal 366 (e.g., at terminal G2) as a function of time.

As shown in FIG. 7 , the secondary controller 308 receives the voltagesignal 362 (e.g., V_(DR)) at the terminal 390, and determines whetherthe voltage signal 362 exceeds a first reference voltage 829 (e.g.,V_(ref1)) according to some embodiments. For example, the firstreference voltage 829 (e.g., V_(ref1)) is higher than a first thresholdvoltage 828 (e.g., V_(th1)), and the first threshold voltage 828 (e.g.,V_(th1)) is higher than a second threshold voltage 830 (e.g., V_(th2)).In another example, the first reference voltage 829 (e.g., V_(ref1)) ishigher than the ground voltage 372 (e.g., zero volt), and both the firstthreshold voltage 828 (e.g., V_(th1)) and the second threshold voltage830 (e.g., V_(th2)) are lower than the ground voltage 372 (e.g., zerovolt). In yet another example, the first reference voltage 829 (e.g.,V_(ref1)) is equal to about 15 V.

In one embodiment, if the voltage signal 362 has been determined by thesecondary controller 308 to exceed the first reference voltage 829, thesecondary controller 308, in response to the voltage signal 362 (e.g.,V_(DR)) decreasing from a value higher than the first reference voltage829 to a value lower than both the first threshold voltage 828 (e.g.,V_(th1)) and the second threshold voltage 830 (e.g., V_(th2)), changesthe signal 366 from a logic low level to a logic high level in order toturn on the transistor 310. In another embodiment, if the voltage signal362 has not been determined by the secondary controller 308 to exceedthe first reference voltage 829, the secondary controller 308 does notchange the signal 366 from the logic low level to the logic high leveleven if the voltage signal 362 (e.g., V_(DR)) decreasing to a value thatis lower than both the first threshold voltage 828 (e.g., V_(th1)) andthe second threshold voltage 830 (e.g., V_(th2)), so that the transistor310 remains off.

For example, a switching period of the switch 330 includes an on-timeperiod during which the switch 330 is closed (e.g., on) and an off-timeperiod during which the switch 330 is open (e.g., off). In anotherexample, as shown in FIG. 7 , an on-time period of the switch 330 (e.g.,T_(on)) starts at time t₂₄ and ends at time t₂₅, and an off-time periodof the switch 330 (e.g., T_(off)) starts at the time t₂₅ and ends attime t₃₀. In yet another example, a demagnetization period (e.g.,T_(demag)) associated with the transformer including the primary winding304 and the secondary winding 306 starts at the time t₂₅ and ends beforeor at the time t₃₀. In yet another example, t₂₄≤t₂₅≤t₃₀.

In one embodiment, during the on-time period (e.g., T_(on)), the switch330 is closed (e.g., being turned on) as shown by the waveform 802, andthe energy is stored in the transformer that includes the primarywinding 304 and the secondary winding 306. For example, the secondarycurrent 352 has a low value (e.g., nearly zero). In another example, thevoltage signal 362 (e.g., V_(DR)) received by the secondary controller308 has a value 818 which is higher than zero (e.g., as shown by thewaveform 808). In yet another example, the signal 366 is at the logiclow level (e.g., as shown by the waveform 810), and the transistor 310is off. In yet another example, during the on-time period (e.g.,T_(on)), the channel current 368 of the transistor 310 has a low value(e.g., nearly zero) and the body-diode current 370 of the transistor 310has a low value (e.g., nearly zero).

In another embodiment, at the end of the on-time period (e.g., at thetime t₂₅), the switch 330 is open (e.g., being turned off) as shown bythe waveform 802, and the energy is transferred to the secondary side.For example, the secondary current 352 increases (e.g., at the timet₂₅). In another example, the voltage signal 362 (e.g., V_(DR))decreases from the value 818 to a value 826 (e.g., as shown by thewaveform 808). In yet another example, the value 826 is lower than boththe first threshold voltage 828 (e.g., V_(th1)) and the second thresholdvoltage 830 (e.g., V_(th2)). In yet another example, both the firstthreshold voltage 828 (e.g., V_(th1)) and the second threshold voltage830 (e.g., V_(th2)) are lower than the ground voltage 372 (e.g., zerovolt). In yet another example, the first threshold voltage 828 (e.g.,V_(th1)) is equal to about −300 mV, and the second threshold voltage 830(e.g., V_(th2)) is equal to about −10 mV. In yet another example, thebody diode 374 of the transistor 310 begins to conduct, and thebody-diode current 370 of the body diode 374 increases.

According to certain embodiments, the secondary controller 308 receivesthe voltage signal 362 (e.g., V_(DR)) at the terminal 390, anddetermines whether the voltage signal 362 exceeds the first referencevoltage 829 (e.g., V_(ref1)). In one embodiment, the first referencevoltage 829 (e.g., V_(ref1)) is higher than the first threshold voltage828 (e.g., V_(th1)), and the first threshold voltage 828 (e.g., V_(th1))is higher than the second threshold voltage 830 (e.g., V_(th2)). Forexample, the first reference voltage 829 (e.g., V_(ref1)) is equal toabout 15 V. In another embodiment, if the voltage signal 362 (e.g., thevalue 818) has been determined to exceed the first reference voltage 829(e.g., between the time t₂₄ and the time t₂₅ as shown by the waveform808), the secondary controller 308, in response to the voltage signal362 (e.g., V_(DR)) decreasing from a value (e.g., the value 818) higherthan the first reference voltage 829 to a value (e.g., the value 826)lower than both the first threshold voltage 828 (e.g., V_(th1)) and thesecond threshold voltage 830 (e.g., V_(th2)), changes the signal 366from the logic low level to the logic high level (e.g., at the time t₂₅as shown by the waveform 810, or at a time after the time t₂₅) in orderto turn on the transistor 310. In yet another embodiment, if the voltagesignal 362 (e.g., the value 818) has been determined to exceed the firstreference voltage 829 (e.g., between the time t₂₄ and the time t₂₅ asshown by the waveform 808), the secondary controller 308, in response tothe voltage signal 362 (e.g., V_(DR)) decreasing from a value (e.g., thevalue 818) higher than the first reference voltage 829 to a value (e.g.,the value 826) lower than the second threshold voltage 830 (e.g.,V_(th2)), changes the signal 366 from the logic low level to the logichigh level (e.g., at the time t₂₅ as shown by the waveform 810, or at atime after the time t₂₅) in order to turn on the transistor 310.

For example, there is a delay (e.g., T_(d)) between the time at whichthe voltage signal 362 (e.g., V_(DR)) decreases from the value 818 tothe value 826 and the time at which the signal 366 changes from thelogic low level to the logic high level. In another example, the delay(e.g., T_(d)) is zero. In yet another example, after the transistor 310is turned on, the channel current 368 of the transistor 310 increases.In yet another example, the secondary current 352 is equal to a sum ofthe channel current 368 and the body-diode current 370.

In yet another embodiment, if the voltage signal 362 has not beendetermined to exceed the first reference voltage 829, the secondarycontroller 308 keeps the signal 366 at the logic low level in order tokeep the transistor 310 to be turned off, regardless of whether thevoltage signal 362 (e.g., V_(DR)) decreases to a value lower than boththe first threshold voltage 828 (e.g., V_(th1)) and the second thresholdvoltage 830 (e.g., V_(th2)). In yet another embodiment, if the voltagesignal 362 has not been determined to exceed the first reference voltage829, the secondary controller 308 keeps the signal 366 at the logic lowlevel in order to keep the transistor 310 to be turned off, regardlessof whether the voltage signal 362 (e.g., V_(DR)) decreases to a valuelower than the second threshold voltage 830 (e.g., V_(th2)).

According to one embodiment, during the demagnetization period, theswitch 330 remains open (e.g., off) as shown by the waveform 802. Forexample, the secondary current 352 decreases. In another example, if thevoltage signal 362 (e.g., V_(DR)) becomes larger than the firstthreshold voltage 828 (e.g., as shown by the waveform 808), the signal366 changes from the logic high level to the logic low level (e.g., asshown by the waveform 810). In yet another example, the transistor 310is turned off, and the channel current 368 of the transistor 310decreases to a low value (e.g., nearly zero). In yet another example,the body-diode current 370 of the transistor 310 flows through the bodydiode 374 of the transistor 310, and then decreases to a low value. Inyet another example, the demagnetization period ends before the timet₃₀. In yet another example, immediately after the end of thedemagnetization period, the voltage signal 362 increases to a value 819as shown by a rising edge in the waveform 808.

According to some embodiments, the secondary controller 308 receives thevoltage signal 362 (e.g., V_(DR)) at the terminal 390, and determineswhether the voltage signal 362 exceeds a first reference voltage 829(e.g., V_(ref1)). In one embodiment, the first reference voltage 829(e.g., V_(ref1)) is higher than the first threshold voltage 828 (e.g.,V_(th1)), and the first threshold voltage 828 (e.g., V_(th1)) is higherthan the second threshold voltage 830 (e.g., V_(th2)). For example, thefirst reference voltage 829 (e.g., V_(ref1)) is equal to about 15 V. Inanother embodiment, if the voltage signal 362 (e.g., the value 819) hasnot been determined to exceed the first reference voltage 829 (e.g.,after the time t₂₅ but before the time t₃₀ as shown by the waveform808), the secondary controller 308 does not change the signal 366 fromthe logic low level to the logic high level even if the voltage signal362 (e.g., V_(DR)) decreasing to a value (e.g., the value 827) that islower than both the first threshold voltage 828 (e.g., V_(th1)) and thesecond threshold voltage 830 (e.g., V_(th2)), so that the transistor 310remains off.

According to yet another embodiment of the present invention, FIG. 7 isa simplified timing diagram for the power conversion system 400 as shownin FIG. 3(B) operating in the discontinuous conduction mode (DCM). Forexample, the waveform 802 represents the power switch 430 being turnedon or off as a function of time, the waveform 808 represents the voltagesignal 462 (e.g., at terminal DR) as a function of time, and thewaveform 810 represents the signal 466 (e.g., at terminal G2) as afunction of time.

As discussed earlier, in one embodiment, if the voltage signal 362(e.g., V_(DR)) becomes larger than the first threshold voltage 828(e.g., as shown by the waveform 808), the signal 366 changes from thelogic high level to the logic low level (e.g., as shown by the waveform810) in order to turn off the transistor 310. For example, such hardturn-off of the transistor 310 often generates ringing at the drain ofthe transistor 310 because the left-over energy in the transformer thatincludes the primary winding 304 and the secondary winding 306 goes outthrough the parasitic body diode 374 of the transistor 310 and resonantwith the parasitic capacitor of the transistor 310 and the inductance ofthe transformer. In another example, these resonant rings (e.g., ringsas shown by the waveform 808 before the time t₃₀) can reach a value(e.g., the value 827) that is lower than both the first thresholdvoltage 828 (e.g., V_(th1)) and the second threshold voltage 830 (e.g.,V_(th2)).

Also as discussed earlier, in another embodiment, the secondarycontroller 308 determines whether the voltage signal 362 (e.g., V_(DR))exceeds the first reference voltage 829 (e.g., V_(ref1)), and based onthe result of this determination, further decides whether to turn offthe transistor 310 in response to the voltage signal 362 (e.g., V_(DR))decreasing to a value that is lower than both the first thresholdvoltage 828 (e.g., V_(th1)) and the second threshold voltage 830 (e.g.,V_(th2)). For example, if the AC input voltage on the primary side has alarge amplitude, the value 818 of the voltage signal 362 is higher thanthe value 819 of the voltage signal 362 as shown by the waveform 808;therefore, the first reference voltage 829 (e.g., V_(ref1)) can beselected to be smaller than the value 818 but larger than the value 819,in order to avoid mis-triggering the secondary controller 308 by theresonant rings (e.g., rings as shown by the waveform 808 before the timet₃₀). In another example, such mis-triggering may result innon-synchronization of the secondary-side rectifier and instability ofthe output voltage 350.

As discussed above and further emphasized here, FIG. 7 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the power conversion system 300 as shownin FIG. 3(A) or the power conversion system 400 as shown in FIG. 3(B)operating in other modes, such as a continuous conduction mode and thecritical conduction mode (e.g., the quasi-resonant mode), can alsoimplement the scheme as illustrated in FIG. 7 .

According to certain embodiments, the scheme as illustrated in FIG. 7 isimplemented in the continuous conduction mode. In one embodiment, if thevoltage signal 362 has been determined by the secondary controller 308to exceed the first reference voltage 829, the secondary controller 308,in response to the voltage signal 362 (e.g., V_(DR)) decreasing from avalue higher than the first reference voltage 829 to a value lower thanboth the first threshold voltage 828 (e.g., V_(th1)) and the secondthreshold voltage 830 (e.g., V_(th2)), changes the signal 366 from thelogic low level to the logic high level in order to turn on thetransistor 310. In another embodiment, if the voltage signal 362 has notbeen determined by the secondary controller 308 to exceed the firstreference voltage 829, the secondary controller 308 does not change thesignal 366 from the logic low level to the logic high level even if thevoltage signal 362 (e.g., V_(DR)) decreasing to a value that is lowerthan both the first threshold voltage 828 (e.g., V_(th1)) and the secondthreshold voltage 830 (e.g., V_(th2)), so that the transistor 310remains off. In yet another embodiment, the controller 302 turns on thetransistor 330 before the demagnetization period ends (e.g., thecontroller 302 turns on the transistor 330 before the secondary current352 drops to zero), and in response, the signal 362 (e.g., V_(DR))increases. In yet another example, the secondary controller 308 detectsa rising edge of the signal 362 and changes the signal 366 to turn offthe transistor 310.

FIG. 8 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the waveform902 represents the power switch 330 being turned on or off as a functionof time, the waveform 908 represents the voltage signal 362 (e.g.,V_(DR) at terminal DR) as a function of time, and the waveform 910represents the signal 366 (e.g., at terminal G2) as a function of time.

As shown in FIG. 8 , the secondary controller 308 receives the voltagesignal 362 (e.g., V_(DR)) at the terminal 390, and determines whetherthe voltage signal 362 exceeds the second reference voltage 929 (e.g.,V_(ref2)) according to some embodiments. In one embodiment, if thevoltage signal 362 is determined to exceed the second reference voltage929 (e.g., V_(ref2)), the secondary controller 308 further determinesthe time duration when the voltage signal 362 remains exceeding thesecond reference voltage 929 (e.g., V_(ref2)), and determines whetherthe time duration is longer than a first threshold time period (e.g.,T_(th1)). For example, the second reference voltage 929 (e.g., V_(ref2))is lower than the first reference voltage 829 (e.g., V_(ref1)) that hasbeen shown in FIG. 7 . In another example, the second reference voltage929 (e.g., V_(ref2)) is higher than the ground voltage 372 (e.g., zerovolt), and both the first threshold voltage 928 (e.g., V_(th1)) and thesecond threshold voltage 930 (e.g., V_(th2)) are lower than the groundvoltage 372 (e.g., zero volt).

In another embodiment, if the time duration when the voltage signal 362remains exceeding the second reference voltage 929 (e.g., V_(ref2)) isdetermined to be longer than the first threshold time period (e.g.,T_(th1)), the secondary controller 308, in response to the voltagesignal 362 (e.g., V_(DR)) decreasing from a value higher than the secondreference voltage 929 to a value lower than both the first thresholdvoltage 928 (e.g., V_(th1)) and the second threshold voltage 930 (e.g.,V_(th2)), changes the signal 366 from the logic low level to the logichigh level in order to turn on the transistor 310. In yet anotherembodiment, if the time duration when the voltage signal 362 remainsexceeding the second reference voltage 929 (e.g., V_(ref2)) is notdetermined to be longer than the first threshold time period (e.g.,T_(th1)), the secondary controller 308 does not change the signal 366from the logic low level to the logic high level even if the voltagesignal 362 (e.g., V_(DR)) decreasing to a value that is lower than boththe first threshold voltage 928 (e.g., V_(th1)) and the second thresholdvoltage 930 (e.g., V_(th2)), so that the transistor 310 remains off.

For example, a switching period of the switch 330 includes an on-timeperiod during which the switch 330 is closed (e.g., on) and an off-timeperiod during which the switch 330 is open (e.g., off). In anotherexample, as shown in FIG. 8 , an on-time period of the switch 330 (e.g.,T_(on)) starts at time t₃₄ and ends at time t₃₅, and an off-time periodof the switch 330 (e.g., T_(off)) starts at the time t₃₅ and ends attime t₄₀. In yet another example, a demagnetization period (e.g.,T_(demag)) associated with the transformer including the primary winding304 and the secondary winding 306 starts at the time t₃₅ and ends beforeor at the time t₄₀. In yet another example, t₃₄≤t₃₅≤t₄₀.

In one embodiment, during the on-time period (e.g., T_(on)), the switch330 is closed (e.g., being turned on) as shown by the waveform 902, andthe energy is stored in the transformer that includes the primarywinding 304 and the secondary winding 306. For example, the secondarycurrent 352 has a low value (e.g., nearly zero). In another example, thevoltage signal 362 (e.g., V_(DR)) received by the secondary controller308 has a value 918 which is higher than zero (e.g., as shown by thewaveform 908). In yet another example, the signal 366 is at the logiclow level (e.g., as shown by the waveform 910), and the transistor 310is off. In yet another example, during the on-time period (e.g.,T_(on)), the channel current 368 of the transistor 310 has a low value(e.g., nearly zero) and the body-diode current 370 of the transistor 310has a low value (e.g., nearly zero).

In another embodiment, at the end of the on-time period (e.g., at thetime t₃₅), the switch 330 is open (e.g., being turned off) as shown bythe waveform 902, and the energy is transferred to the secondary side.For example, the secondary current 352 increases (e.g., at the timet₃₅). In another example, the voltage signal 362 (e.g., V_(DR))decreases from the value 918 to a value 926 (e.g., as shown by thewaveform 908). In yet another example, the value 926 is lower than boththe first threshold voltage 928 (e.g., V_(th1)) and the second thresholdvoltage 930 (e.g., V_(th2)). In yet another example, both the firstthreshold voltage 928 (e.g., V_(th1)) and the second threshold voltage930 (e.g., V_(th2)) are lower than the ground voltage 372 (e.g., zerovolt). In yet another example, the first threshold voltage 928 (e.g.,V_(th1)) is equal to about −300 mV, and the second threshold voltage 930(e.g., V_(th2)) is equal to about −10 mV. In yet another example, thebody diode 374 of the transistor 310 begins to conduct, and thebody-diode current 370 of the body diode 374 increases.

According to certain embodiments, the secondary controller 308 receivesthe voltage signal 362 (e.g., V_(DR)) at the terminal 390, anddetermines whether the voltage signal 362 exceeds the second referencevoltage 929 (e.g., V_(ref2)). In one embodiment, if the voltage signal362 is determined to exceed (e.g., at the time t₃₄) the second referencevoltage 929 (e.g., V_(ref2)), the secondary controller 308 furtherdetermines the time duration (e.g., the time duration T_(A) from thetime t₃₄ to the time t₃₅) when the voltage signal 362 remains exceedingthe second reference voltage 929 (e.g., V_(ref2)), and determineswhether the time duration (e.g., the time duration T_(A)) is longer thana first threshold time period (e.g., T_(th1)). For example, the secondreference voltage 929 (e.g., V_(ref2)) is lower than the first referencevoltage 829 (e.g., V_(ref1)) that has been shown in FIG. 7 . In anotherembodiment, if the time duration (e.g., the time duration T_(A)) isdetermined to be longer than the first threshold time period (e.g.,T_(th1)), the secondary controller 308, in response to the voltagesignal 362 (e.g., V_(DR)) decreasing from a value (e.g., the value 918)higher than the second reference voltage 929 to a value (e.g., the value926) lower than both the first threshold voltage 928 (e.g., V_(th1)) andthe second threshold voltage 930 (e.g., V_(th2)), changes the signal 366from the logic low level to the logic high level (e.g., at the time t₃₅as shown by the waveform 910, or at a time after t₃₅) in order to turnon the transistor 310. In yet another embodiment, if the time duration(e.g., the time duration T_(A)) is determined to be longer than thefirst threshold time period (e.g., T_(th1)), the secondary controller308, in response to the voltage signal 362 (e.g., V_(DR)) decreasingfrom a value (e.g., the value 918) higher than the second referencevoltage 929 to a value (e.g., the value 926) lower than the secondthreshold voltage 930 (e.g., V_(th2)), changes the signal 366 from thelogic low level to the logic high level (e.g., at the time t₃₅ as shownby the waveform 910, or at a time after t₃₅) in order to turn on thetransistor 310.

For example, the time duration T_(A) is longer than the first thresholdtime period T_(th1). In another example, the first threshold voltage 928(e.g., V_(th1)) is the same as the first threshold voltage 828 (e.g.,V_(th1)) that has been shown in FIG. 7 , and the second thresholdvoltage 930 (e.g., V_(th2)) is the same as the second threshold voltage830 (e.g., V_(th2)) that has been shown in FIG. 7 . In another example,there is a delay (e.g., T_(d)) between the time at which the voltagesignal 362 (e.g., V_(DR)) decreases from the value 918 to the value 926and the time at which the signal 366 changes from the logic low level tothe logic high level. In yet another example, the delay (e.g., T_(d)) iszero.

In yet another embodiment, after the transistor 310 is turned on, thechannel current 368 of the transistor 310 increases. In yet anotherembodiment, the secondary current 352 is equal to a sum of the channelcurrent 368 and the body-diode current 370.

In yet another embodiment, if the time duration (e.g., the time durationT_(A)) is not determined to be longer than the first threshold timeperiod (e.g., T_(th1)), the secondary controller 308 keeps the signal366 at the logic low level in order to keep the transistor 310 to beturned off, regardless of whether the voltage signal 362 (e.g., V_(DR))decreases to a value lower than both the first threshold voltage 928(e.g., V_(th1)) and the second threshold voltage 930 (e.g., V_(th2)). Inyet another embodiment, if the time duration (e.g., the time durationT_(A)) is not determined to be longer than the first threshold timeperiod (e.g., T_(th1)), the secondary controller 308 keeps the signal366 at the logic low level in order to keep the transistor 310 to beturned off, regardless of whether the voltage signal 362 (e.g., V_(DR))decreases to a value lower than the second threshold voltage 930 (e.g.,V_(th2))

According to one embodiment, during the demagnetization period, theswitch 330 remains open (e.g., off) as shown by the waveform 902. Forexample, the secondary current 352 decreases. In another example, if thevoltage signal 362 (e.g., V_(DR)) becomes larger than the firstthreshold voltage 928 (e.g., as shown by the waveform 908), the signal366 changes from the logic high level to the logic low level (e.g., asshown by the waveform 910). In yet another example, the transistor 310is turned off, and the channel current 368 of the transistor 310decreases to a low value (e.g., nearly zero). In yet another example,the body-diode current 370 of the transistor 310 flows through the bodydiode 374 of the transistor 310, and then decreases to a low value. Inyet another example, the demagnetization period ends before the timet₄₀. In yet another example, immediately after the end of thedemagnetization period, the voltage signal 362 increases to a value 919as shown by a rising edge in the waveform 908.

According to certain embodiments, the secondary controller 308 receivesthe voltage signal 362 (e.g., V_(DR)) at the terminal 390, anddetermines whether the voltage signal 362 exceeds the second referencevoltage 929 (e.g., V_(ref2)). In one embodiment, if the voltage signal362 is determined to exceed (e.g., at time t₃₆) the second referencevoltage 929 (e.g., V_(ref2)), the secondary controller 308 furtherdetermines the time duration (e.g., the time duration T_(B) from thetime t₃ to time t₃₇) when the voltage signal 362 remains exceeding thesecond reference voltage 929 (e.g., V_(ref2)), and determines whetherthe time duration (e.g., the time duration T_(B)) is longer than a firstthreshold time period (e.g., T_(th1)). In another embodiment, if thetime duration (e.g., the time duration T_(B)) is not determined to belonger than the first threshold time period (e.g., T_(th1)), thesecondary controller 308 does not change the signal 366 from the logiclow level to the logic high level even if the voltage signal 362 (e.g.,V_(DR)) decreasing to a value (e.g., the value 927) that is lower thanboth the first threshold voltage 928 (e.g., V_(th1)) and the secondthreshold voltage 930 (e.g., V_(th2)), so that the transistor 310remains off. For example, the time duration T_(B) is shorter than thefirst threshold time period T_(th1).

According to yet another embodiment of the present invention, FIG. 8 isa simplified timing diagram for the power conversion system 400 as shownin FIG. 3(B) operating in the discontinuous conduction mode (DCM). Forexample, the waveform 902 represents the power switch 430 being turnedon or off as a function of time, the waveform 908 represents the voltagesignal 462 (e.g., at terminal DR) as a function of time, and thewaveform 910 represents the signal 466 (e.g., at terminal G2) as afunction of time.

As discussed earlier, in one embodiment, if the voltage signal 362(e.g., V_(DR)) becomes larger than the first threshold voltage 928(e.g., as shown by the waveform 908), the signal 366 changes from thelogic high level to the logic low level (e.g., as shown by the waveform910) in order to turn off the transistor 310. For example, such hardturn-off of the transistor 310 often generates ringing at the drain ofthe transistor 310 because the left-over energy in the transformer thatincludes the primary winding 304 and the secondary winding 306 goes outthrough the parasitic body diode 374 of the transistor 310 and resonantwith the parasitic capacitor of the transistor 310 and the inductance ofthe transformer. In another example, these resonant rings (e.g., ringsas shown by the waveform 908 before the time t₄₀) can reach a value(e.g., the value 927) that is lower than both the first thresholdvoltage 928 (e.g., V_(th1)) and the second threshold voltage 930 (e.g.,V_(th2)).

Also as discussed earlier, in another embodiment, the secondarycontroller 308 determines whether the time duration when the voltagesignal 362 remains exceeding the second reference voltage 929 (e.g.,V_(ref2)) is longer than the first threshold time period (e.g.,T_(th1)). For example, based on the result of this determination, thesecondary controller 308 further decides whether to turn off thetransistor 310 in response to the voltage signal 362 (e.g., V_(DR))decreasing to a value that is lower than both the first thresholdvoltage 928 (e.g., V_(th1)) and the second threshold voltage 930 (e.g.,V_(th2)).

In another example, if the AC input voltage on the primary side has asmall amplitude, the value 918 of the voltage signal 362 and the value919 of the voltage signal 362 as shown by the waveform 908 areapproximately equal; therefore, it is difficult to select a value forthe first reference voltage 829 (e.g., V_(ref1)) that is smaller thanthe value 918 but larger than the value 919, but a value for the secondreference voltage 929 (e.g., V_(ref2)) can be selected so that the timeduration when the voltage signal 362 remains exceeding the secondreference voltage 929 (e.g., V_(ref2)) can be used to avoidmis-triggering the secondary controller 308 by the resonant rings (e.g.,rings as shown by the waveform 908 before the time t₄₀). In anotherexample, such mis-triggering may result in non-synchronization of thesecondary-side rectifier and instability of the output voltage 350.

As discussed above and further emphasized here, FIG. 8 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the power conversion system 300 as shownin FIG. 3(A) or the power conversion system 400 as shown in FIG. 3(B)operating in other modes, such as a continuous conduction mode and thecritical conduction mode (e.g., the quasi-resonant mode), can alsoimplement the scheme as illustrated in FIG. 8 .

According to certain embodiments, the scheme as illustrated in FIG. 8 isimplemented in the continuous conduction mode. In one embodiment, if thetime duration when the voltage signal 362 remains exceeding the secondreference voltage 929 (e.g., V_(ref2)) is determined to be longer thanthe first threshold time period (e.g., T_(th1)), the secondarycontroller 308, in response to the voltage signal 362 (e.g., V_(DR))decreasing from a value higher than the second reference voltage 929 toa value lower than both the first threshold voltage 928 (e.g., V_(th1))and the second threshold voltage 930 (e.g., V_(th2)), changes the signal366 from the logic low level to the logic high level in order to turn onthe transistor 310. In another embodiment, if the time duration when thevoltage signal 362 remains exceeding the second reference voltage 929(e.g., V_(ref2)) is not determined to be longer than the first thresholdtime period (e.g., T_(th1)), the secondary controller 308 does notchange the signal 366 from the logic low level to the logic high leveleven if the voltage signal 362 (e.g., V_(DR)) decreasing to a value thatis lower than both the first threshold voltage 928 (e.g., V_(th1)) andthe second threshold voltage 930 (e.g., V_(th2)), so that the transistor310 remains off. In yet another embodiment, the controller 302 turns onthe transistor 330 before the demagnetization period ends (e.g., thecontroller 302 turns on the transistor 330 before the secondary current352 drops to zero), and in response, the signal 362 (e.g., V_(DR))increases. In yet another example, the secondary controller 308 detectsa rising edge of the signal 362 and changes the signal 366 to turn offthe transistor 310.

According to some embodiments, as shown in FIG. 8 , the secondarycontroller 308 receives the voltage signal 362 (e.g., V_(DR)) at theterminal 390, and determines whether the voltage signal 362 is lowerthan the first reference voltage 829 (e.g., V_(ref1)) but exceeds thesecond reference voltage 929 (e.g., V_(ref2)). In one embodiment, if thevoltage signal 362 is determined to be lower than the first referencevoltage 829 (e.g., V_(ref1)) but to exceed the second reference voltage929 (e.g., V_(ref2)), the secondary controller 308 further determinesthe time duration when the voltage signal 362 remains lower than thefirst reference voltage 829 (e.g., V_(ref1)) but exceeding the secondreference voltage 929 (e.g., V_(ref2)), and determines whether the timeduration is longer than the first threshold time period (e.g., T_(th1)).In another embodiment, if the time duration when the voltage signal 362remains lower than the first reference voltage 829 (e.g., V_(ref1)) butexceeding the second reference voltage 929 (e.g., V_(ref2)) isdetermined to be longer than the first threshold time period (e.g.,T_(th1)), the secondary controller 308, in response to the voltagesignal 362 (e.g., V_(DR)) decreasing from a value higher than the secondreference voltage 929 to a value lower than both the first thresholdvoltage 928 (e.g., V_(th1)) and the second threshold voltage 930 (e.g.,V_(th2)), changes the signal 366 from the logic low level to the logichigh level in order to turn on the transistor 310. In yet anotherembodiment, if the time duration when the voltage signal 362 remainslower than the first reference voltage 829 (e.g., V_(ref1)) butexceeding the second reference voltage 929 (e.g., V_(ref2)) is notdetermined to be longer than the first threshold time period (e.g.,T_(th1)), the secondary controller 308 does not change the signal 366from the logic low level to the logic high level even if the voltagesignal 362 (e.g., V_(DR)) decreasing to a value that is lower than boththe first threshold voltage 928 (e.g., V_(th1)) and the second thresholdvoltage 930 (e.g., V_(th2)), so that the transistor 310 remains off.

FIG. 9 is a simplified timing diagram for the power conversion system300 as shown in FIG. 3(A) operating in the discontinuous conduction mode(DCM) according to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, the waveform1002 represents the power switch 330 being turned on or off as afunction of time, the waveform 1008 represents the voltage signal 362(e.g., V_(DR) at terminal DR) as a function of time, and the waveform1010 represents the signal 366 (e.g., at terminal G2) as a function oftime.

As shown in FIG. 9 , the secondary controller 308 receives the voltagesignal 362 (e.g., V_(DR)) at the terminal 390, determines the timeduration from the time when the voltage signal 362 exceeds a thirdreference voltage 1029 (e.g., V_(ref3)) to the time when the voltagesignal 362 drops below a fourth reference voltage 1031 (e.g., V_(ref4)),and further determines whether the time duration is longer than a secondthreshold time period (e.g., T_(th2)). In one embodiment, if the timeduration is determined to be longer than the second threshold timeperiod (e.g., T_(th2)), the secondary controller 308, in response to thevoltage signal 362 (e.g., V_(DR)) decreasing from a value higher thanthe third reference voltage 1029 to a value lower than both a firstthreshold voltage 1028 (e.g., V_(th1)) and a second threshold voltage1030 (e.g., V_(th2)), changes the signal 366 from the logic low level tothe logic high level in order to turn on the transistor 310. In anotherembodiment, if the time duration is not determined to be longer than thesecond threshold time period (e.g., T_(th2)), the secondary controller308 does not change the signal 366 from the logic low level to the logichigh level even if the voltage signal 362 (e.g., V_(DR)) decreasing to avalue that is lower than both the first threshold voltage 1028 (e.g.,V_(th1)) and the second threshold voltage 1030 (e.g., V_(th2)), so thatthe transistor 310 remains off.

For example, a switching period of the switch 330 includes an on-timeperiod during which the switch 330 is closed (e.g., on) and an off-timeperiod during which the switch 330 is open (e.g., off). In anotherexample, as shown in FIG. 9 , an on-time period of the switch 330 (e.g.,T_(on)) starts at time t₄₄ and ends at time t₄₅, or starts at time t₅₀and ends at time t₅₁. In yet another example, as shown in FIG. 9 , anoff-time period of the switch 330 (e.g., T_(off)) starts at the time t₄₅and ends at the time t₅₀. In yet another example, a demagnetizationperiod (e.g., T_(demag)) associated with the transformer including theprimary winding 304 and the secondary winding 306 starts at the time t₄₅and ends before or at the time t₅₀. In yet another example,t₄₄≤t₄₅≤t₅₀≤t₅₁.

In one embodiment, during the on-time period (e.g., T_(on)), the switch330 is closed (e.g., being turned on) as shown by the waveform 1002, andthe energy is stored in the transformer that includes the primarywinding 304 and the secondary winding 306. For example, the secondarycurrent 352 has a low value (e.g., nearly zero). In another example, thevoltage signal 362 (e.g., V_(DR)) received by the secondary controller308 has a value 1018 which is higher than zero (e.g., as shown by thewaveform 1008). In yet another example, the signal 366 is at the logiclow level (e.g., as shown by the waveform 1010), and the transistor 310is off. In yet another example, during the on-time period (e.g.,T_(on)), the channel current 368 of the transistor 310 has a low value(e.g., nearly zero) and the body-diode current 370 of the transistor 310has a low value (e.g., nearly zero).

In another embodiment, at the end of the on-time period (e.g., at thetime t₄₅ or at the time t₅₁), the switch 330 is open (e.g., being turnedoff) as shown by the waveform 1002, and the energy is transferred to thesecondary side. For example, the secondary current 352 increases (e.g.,at the time t₄₅ or at the time t₅₁). In another example, the voltagesignal 362 (e.g., V_(DR)) decreases from the value 1018 to a value 1026(e.g., as shown by the waveform 1008). In yet another example, the value1026 is lower than both the first threshold voltage 1028 (e.g., V_(th1))and the second threshold voltage 1030 (e.g., V_(th2)). In yet anotherexample, both the first threshold voltage 1028 (e.g., V_(th1)) and thesecond threshold voltage 1030 (e.g., V_(th2)) are lower than the groundvoltage 372 (e.g., zero volt). In yet another example, the firstthreshold voltage 1028 (e.g., V_(th1)) is equal to about −300 mV, andthe second threshold voltage 1030 (e.g., V_(th2)) is equal to about −10mV. In yet another example, the body diode 374 of the transistor 310begins to conduct, and the body-diode current 370 of the body diode 374increases.

According to some embodiments, the secondary controller 308 receives thevoltage signal 362 (e.g., V_(DR)) at the terminal 390, determines thetime duration (e.g., time duration T_(C)) from the time (e.g., time t₄₆)when the voltage signal 362 exceeds the third reference voltage 1029(e.g., V_(ref3)) to the time (e.g., time t₄₇) when the voltage signal362 drops below the fourth reference voltage 1031 (e.g., V_(ref4)), andfurther determines whether the time duration (e.g., the time durationT_(C)) is longer than the second threshold time period (e.g., T_(th2)).For example, the fourth reference voltage 1031 (e.g., V_(ref4)) is lowerthan the third reference voltage 1029 (e.g., V_(ref1)), which is lowerthan the first reference voltage 829 (e.g., V_(ref1)) that has beenshown in FIG. 7 and is also lower than the second reference voltage 929(e.g., V_(ref2)) that has been shown in FIG. 8 . In another example, thethird reference voltage 1029 (e.g., V_(ref3)) is higher than the fourthreference voltage 1031 (e.g., V_(ref4)), the fourth reference voltage1031 (e.g., V_(ref4)) is higher than the first threshold voltage 1028(e.g., V_(th1)), and the first threshold voltage 1028 (e.g., V_(th1)) ishigher than the second threshold voltage 1030 (e.g., V_(th2)). In yetanother example, both the third reference voltage 1029 (e.g., V_(ref3))and the fourth reference voltage 1031 (e.g., V_(ref4)) are higher thanthe ground voltage 372 (e.g., zero volt), and both the first thresholdvoltage 1028 (e.g., V_(th1)) and the second threshold voltage 1030(e.g., V_(th2)) are lower than the ground voltage 372 (e.g., zero volt).In yet another example, the time duration T_(C) is shorter than thesecond threshold time period T_(th2).

In one embodiment, if the time duration (e.g., the time duration T_(C))is not determined to be longer than the second threshold time period(e.g., T_(th2)), the secondary controller 308 does not change the signal366 from the logic low level to the logic high level even if the voltagesignal 362 (e.g., V_(DR)) decreasing to a value (e.g., a value 1027)that is lower than both the first threshold voltage 1028 (e.g., V_(th1))and the second threshold voltage 1030 (e.g., V_(th2)), so that thetransistor 310 remains off. For example, the first threshold voltage1028 (e.g., V_(th1)) is the same as the first threshold voltage 928(e.g., V_(th1)) that has been shown in FIG. 8 and is also the same asthe first threshold voltage 828 (e.g., V_(th1)) that has been shown inFIG. 7 . In another example, the second threshold voltage 1030 (e.g.,V_(th2)) is the same as the second threshold voltage 930 (e.g., V_(th2))that has been shown in FIG. 8 and is also the same as the secondthreshold voltage 830 (e.g., V_(th2)) that has been shown in FIG. 7 .

According to certain embodiments, the secondary controller 308 receivesthe voltage signal 362 (e.g., V_(DR)) at the terminal 390, determinesthe time duration (e.g., time duration T_(D)) from the time (e.g., timet₄₈) when the voltage signal 362 exceeds the third reference voltage1029 (e.g., V_(ref3)) to the time (e.g., the time t₅₁) when the voltagesignal 362 drops below the fourth reference voltage 1031 (e.g.,V_(ref4)), and further determines whether the time duration (e.g., thetime duration T_(D)) is longer than the second threshold time period(e.g., T_(th2)). In one embodiment, if the time duration (e.g., the timeduration T_(D)) is determined to be longer than the second thresholdtime period (e.g., T_(th2)), the secondary controller 308, in responseto the voltage signal 362 (e.g., V_(DR)) decreasing from a value (e.g.,the value 1018) higher than the third reference voltage 1029 to a value(e.g., the value 1026) lower than both the first threshold voltage 1028(e.g., V_(th1)) and the second threshold voltage 1030 (e.g., V_(th2)),changes the signal 366 from the logic low level to the logic high level(e.g., at the time t₅₁ as shown by the waveform 1010, or at a time aftert₅₁) in order to turn on the transistor 310. In another embodiment, ifthe time duration (e.g., the time duration T_(D)) is determined to belonger than the second threshold time period (e.g., T_(th2)), thesecondary controller 308, in response to the voltage signal 362 (e.g.,V_(DR)) decreasing from a value (e.g., the value 1018) higher than thethird reference voltage 1029 to a value (e.g., the value 1026) lowerthan the second threshold voltage 1030 (e.g., V_(th2)), changes thesignal 366 from the logic low level to the logic high level (e.g., atthe time t₅₁ as shown by the waveform 1010, or at a time after t₅₁) inorder to turn on the transistor 310.

For example, the time duration T_(D) is longer than the second thresholdtime period T_(th2). In another example, there is a delay (e.g., T_(d))between the time at which the voltage signal 362 (e.g., V_(DR))decreases from the value 1018 to the value 1026 and the time at whichthe signal 366 changes from the logic low level to the logic high level.In yet another example, the delay (e.g., T_(d)) is zero. In anotherembodiment, after the transistor 310 is turned on, the channel current368 of the transistor 310 increases. In yet another embodiment, thesecondary current 352 is equal to a sum of the channel current 368 andthe body-diode current 370.

In yet another embodiment, if the time duration (e.g., the time durationT_(D)) is not determined to be longer than the second threshold timeperiod (e.g., T_(th2)), the secondary controller 308 keeps the signal366 at the logic low level in order to keep the transistor 310 to beturned off, regardless of whether the voltage signal 362 (e.g., V_(DR))decreases to a value lower than both the first threshold voltage 1028(e.g., V_(th1)) and the second threshold voltage 1030 (e.g., V_(th2)).In yet another embodiment, if the time duration (e.g., the time durationT_(D)) is not determined to be longer than the second threshold timeperiod (e.g., T_(th2)), the secondary controller 308 keeps the signal366 at the logic low level in order to keep the transistor 310 to beturned off, regardless of whether the voltage signal 362 (e.g., V_(DR))decreases to a value lower than the second threshold voltage 1030 (e.g.,V_(th2)).

According to one embodiment, during the demagnetization period, theswitch 330 remains open (e.g., off) as shown by the waveform 1002. Forexample, the secondary current 352 decreases. In another example, if thevoltage signal 362 (e.g., V_(DR)) becomes larger than the firstthreshold voltage 1028 (e.g., as shown by the waveform 1008), the signal366 changes from the logic high level to the logic low level (e.g., asshown by the waveform 1010). In yet another example, the transistor 310is turned off, and the channel current 368 of the transistor 310decreases to a low value (e.g., nearly zero). In yet another example,the body-diode current 370 of the transistor 310 flows through the bodydiode 374 of the transistor 310, and then decreases to a low value. Inyet another example, the demagnetization period starts at the time t₄₅and ends before the time t₅₀, or starts at the time t₅₁. In yet anotherexample, immediately after the end of the demagnetization period, thevoltage signal 362 increases to a value 1019 as shown by a rising edgein the waveform 1008.

According to another embodiment of the present invention, FIG. 9 is asimplified timing diagram for the power conversion system 400 as shownin FIG. 3(B) operating in the discontinuous conduction mode (DCM). Forexample, the waveform 1002 represents the power switch 430 being turnedon or off as a function of time, the waveform 1008 represents thevoltage signal 462 (e.g., at terminal DR) as a function of time, and thewaveform 1010 represents the signal 466 (e.g., at terminal G2) as afunction of time.

As discussed earlier, in one embodiment, if the voltage signal 362(e.g., V_(DR)) becomes larger than the first threshold voltage 1028(e.g., as shown by the waveform 1008), the signal 366 changes from thelogic high level to the logic low level (e.g., as shown by the waveform1010) in order to turn off the transistor 310. For example, such hardturn-off of the transistor 310 often generates ringing at the drain ofthe transistor 310 because the left-over energy in the transformer thatincludes the primary winding 304 and the secondary winding 306 goes outthrough the parasitic body diode 374 of the transistor 310 and resonantwith the parasitic capacitor of the transistor 310 and the inductance ofthe transformer. In another example, these resonant rings (e.g., ringsas shown by the waveform 1008 before the time t₅₀) can reach a value(e.g., the value 927) that is lower than both the first thresholdvoltage 1028 (e.g., V_(th1)) and the second threshold voltage 1030(e.g., V_(th2)).

Also as discussed earlier, in another embodiment, the secondarycontroller 308 determines whether the time duration from the time whenthe voltage signal 362 exceeds the third reference voltage 1029 (e.g.,V_(ref1)) to the time when the voltage signal 362 drops below the fourthreference voltage 1031 (e.g., V_(ref4)) is longer than the secondthreshold time period (e.g., T_(th2)). For example, based on the resultof this determination, the secondary controller 308 further decideswhether to turn off the transistor 310 in response to the voltage signal362 (e.g., V_(DR)) decreasing to a value that is lower than both thefirst threshold voltage 928 (e.g., V_(th1)) and the second thresholdvoltage 930 (e.g., V_(th2)). In another example, if the power conversionsystem 300 is under light load or no load conditions, the time durationT_(A) (e.g., T_(on)) may become shorter than the first threshold timeperiod (e.g., T_(th1)), resulting in missing of the pulse firing and/ornon-synchronization, but such resonant ring pattern can be detected asshown in FIG. 9 .

As discussed above and further emphasized here, FIG. 9 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the power conversion system 300 as shownin FIG. 3(A) or the power conversion system 400 as shown in FIG. 3(B)operating in other modes, such as a continuous conduction mode and thecritical conduction mode (e.g., the quasi-resonant mode), can alsoimplement the scheme as illustrated in FIG. 9 .

According to certain embodiments, the scheme as illustrated in FIG. 9 isimplemented in the continuous conduction mode. In one embodiment, if thetime duration from the time when the voltage signal 362 exceeds thethird reference voltage 1029 (e.g., V_(ref1)) to the time when thevoltage signal 362 drops below the fourth reference voltage 1031 (e.g.,V_(ref4)) is determined to be longer than the second threshold timeperiod (e.g., T_(th2)), the secondary controller 308, in response to thevoltage signal 362 (e.g., V_(DR)) decreasing from a value higher thanthe third reference voltage 1029 to a value lower than both the firstthreshold voltage 1028 (e.g., V_(th1)) and the second threshold voltage1030 (e.g., V_(th2)), changes the signal 366 from the logic low level tothe logic high level in order to turn on the transistor 310. In anotherembodiment, if the time duration from the time when the voltage signal362 exceeds the third reference voltage 1029 (e.g., V_(ref3)) to thetime when the voltage signal 362 drops below the fourth referencevoltage 1031 (e.g., V_(ref4)) is not determined to be longer than thesecond threshold time period (e.g., T_(th2)), the secondary controller308 does not change the signal 366 from the logic low level to the logichigh level even if the voltage signal 362 (e.g., V_(DR)) decreasing to avalue that is lower than both the first threshold voltage 1028 (e.g.,V_(th1)) and the second threshold voltage 1030 (e.g., V_(th2)), so thatthe transistor 310 remains off. In yet another embodiment, thecontroller 302 turns on the transistor 330 before the demagnetizationperiod ends (e.g., the controller 302 turns on the transistor 330 beforethe secondary current 352 drops to zero), and in response, the signal362 (e.g., V_(DR)) increases. In yet another example, the secondarycontroller 308 detects a rising edge of the signal 362 and changes thesignal 366 to turn off the transistor 310.

According to certain embodiments, as shown in FIG. 9 , the secondarycontroller 308 receives the voltage signal 362 (e.g., V_(DR)) at theterminal 390, determines the time duration from the time when thevoltage signal 362 is lower than both the first reference voltage 829(e.g., V_(ref1)) and the second reference voltage 929 (e.g., V_(ref2))but exceeds a third reference voltage 1029 (e.g., V_(ref3)) to the timewhen the voltage signal 362 drops below a fourth reference voltage 1031(e.g., V_(ref4)), and further determines whether the time duration islonger than a second threshold time period (e.g., T_(th2)). For example,V_(ref1)>V_(ref2)>V_(ref3)>V_(ref4). In one embodiment, if the timeduration is determined to be longer than the second threshold timeperiod (e.g., T_(th2)), the secondary controller 308, in response to thevoltage signal 362 (e.g., V_(DR)) decreasing from a value higher thanthe third reference voltage 1029 to a value lower than both the firstthreshold voltage 1028 (e.g., V_(th1)) and the second threshold voltage1030 (e.g., V_(th2)), changes the signal 366 from the logic low level tothe logic high level in order to turn on the transistor 310. In anotherembodiment, if the time duration is not determined to be longer than thesecond threshold time period (e.g., T_(th2)), the secondary controller308 does not change the signal 366 from the logic low level to the logichigh level even if the voltage signal 362 (e.g., V_(DR)) decreasing to avalue that is lower than both the first threshold voltage 1028 (e.g.,V_(th1)) and the second threshold voltage 1030 (e.g., V_(th2)), so thatthe transistor 310 remains off.

FIG. 10 is a simplified diagram showing certain components of thesecondary controller 308 as part of the power conversion system 300according to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The secondary controller308 includes a clamping component 1102, an offset component 1104, arising-edge detection component 1106, comparators 1124, 1210, 1220,1230, and 1240, a falling-edge detection component 1110, a timingcontroller 1112, a logic control component 1114, a gate driver 1116, alight-load detector 1118, a signal generator 1120, an oscillator 1122,an under-voltage-lockout component 1128, and a reference-signalgenerator 1126, an OR gate 1250, a debounce component 1224, and a timercomponent 1234. For example, some components of the secondary controller308 are used for synchronized rectifying, including the clampingcomponent 1102, the offset component 1104, the rising-edge detectioncomponent 1106, the comparators 1124, 1210, 1220, 1230, and 1240, thefalling-edge detection component 1110, the timing controller 1112, thelogic control component 1114, the gate driver 1116, the OR gate 1250,the debounce component 1224, and the timer component 1234. In anotherexample, certain components of the secondary controller 308 are used foroutput voltage detection and control, including the light-load detector1118, the signal generator 1120, the oscillator 1122, thereference-signal generator 1126, the logic control component 1114, andthe gate driver 1116. In yet another example, the components of thesecondary controller 308 that are used for synchronized rectifying andthe components of the secondary controller 308 that are used for outputvoltage detection and control are integrated on a same chip.

In one embodiment, the clamping component 1102 receives the voltagesignal 362 (e.g., V_(DR)) from the terminal 390 (e.g., terminal DR). Forexample, the voltage signal 362 (e.g., V_(DR)) is clamped by theclamping component 1102. In another example, the clamping component 1102is removed from the secondary controller 308. In another embodiment, therising-edge detection component 1106, the comparators 1210, 1220, 1230,and 1240, and the falling-edge detection component 1110 receive a signal1158 which is equal to the voltage signal 362 modified by the offsetcomponent 1104. For example, the offset component 604 is omitted, andthe signal 1158 is the same as the signal 362. In another example, therising-edge detection component 1106 includes a comparator, and thefalling-edge detection component 1110 includes a comparator.

In another embodiment, the comparator 1210 receives the signal 1158 anda first reference voltage 1218 (e.g., the first reference voltage 829),and outputs a signal 1216 to the OR gate. For example, if the signal1158 is larger than the first reference voltage 1218 (e.g., the firstreference voltage 829), the signal 1216 is at a logic high level. Inanother example, if the signal 1158 is smaller than the first referencevoltage 1218 (e.g., the first reference voltage 829), the signal 1216 isat a logic low level. In yet another embodiment, the comparator 1220receives the signal 1158 and a second reference voltage 1228 (e.g., thesecond reference voltage 929), and outputs a signal 1222 to the debouncecomponent 1224. For example, if the signal 1158 is larger than thesecond reference voltage 1228 (e.g., the second reference voltage 929),the signal 1222 is at a logic high level. In another example, if thesignal 1158 is smaller than the second reference voltage 1228 (e.g., thesecond reference voltage 929), the signal 1222 is at a logic low level.

In yet another embodiment, the comparator 1230 receives the signal 1158and a third reference voltage 1238 (e.g., the third reference voltage1029), and outputs a signal 1232 to the timer component 1234. Forexample, if the signal 1158 is larger than the third reference voltage1238 (e.g., the third reference voltage 1029), the signal 1232 is at alogic high level. In another example, if the signal 1158 is smaller thanthe third reference voltage 1238 (e.g., the third reference voltage1029), the signal 1232 is at a logic low level. In yet anotherembodiment, the comparator 1240 receives the signal 1158 and a fourthreference voltage 1248 (e.g., the fourth reference voltage 1031), andoutputs a signal 1242 to the timer component 1234. For example, if thesignal 1158 is larger than the fourth reference voltage 1248 (e.g., thefourth reference voltage 1031), the signal 1242 is at a logic highlevel. In another example, if the signal 1158 is smaller than the fourthreference voltage 1248 (e.g., the fourth reference voltage 1031), thesignal 1242 is at a logic low level.

According to one embodiment, the debounce component 1224 receives thesignal 1222 from the comparator 1220, determines whether the signal 1222indicates that the signal 1158 remains to be larger than the secondreference voltage 1228 (e.g., the second reference voltage 929) for atime duration that is longer than a first threshold time period (e.g.,T_(th1)), and outputs a signal 1226 to the OR gate 1250. For example, ifthe debounce component 1224 determines that the signal 1222 indicatesthat the signal 1158 remains to be larger than the second referencevoltage 1228 (e.g., the second reference voltage 929) for a timeduration that is longer than the first threshold time period (e.g.,T_(th1)), the debounce component 1224 generates the signal 1226 at alogic high level. In another example, if the debounce component 1224determines that the signal 1222 does not indicate that the signal 1158remains to be larger than the second reference voltage 1228 (e.g., thesecond reference voltage 929) for a time duration that is longer thanthe first threshold time period (e.g., T_(th1)), the debounce component1224 generates the signal 1226 at a logic low level.

According to another embodiment, the timer component 1234 receives thesignal 1232 from the comparator 1230 and the signal 1242 from thecomparator 1240, and outputs a signal 1236 to the OR gate 1250. Forexample, the timer component 1234 determines a time duration from thetime when the voltage signal 1158 exceeds the third reference voltage1238 (e.g., the third reference voltage 1029) to the time when thevoltage signal 1158 drops below the fourth reference voltage 1248 (e.g.,the fourth reference voltage 1031). In another example, if thedetermined time duration is longer than a second threshold time period(e.g., T_(th2)), the timer component 1234 generates the signal 1236 at alogic high level. In yet another example, if the determined timeduration is not longer than the second threshold time period (e.g.,T_(th2)), the timer component 1234 generates the signal 1236 at a logiclow level.

According to yet another embodiment, the OR gate 1250 receives thesignals 1216, 1226, and 1236 from the comparator 1210, the debouncecomponent 1224, and the timer component 1234 respectively, and outputs asignal 1252 to the falling-edge detection component 1110 (e.g., acomparator). For example, if any of the signals 1216, 1226, and 1236 isat a logic high level, the OR gate generates the signal 1252 at a logichigh level. In another example, if none of the signals 1216, 1226, and1236 is at the logic high level, the OR gates generates the signal 1252at a logic low level.

In one embodiment, the falling-edge detection component 1110 (e.g., acomparator) receives the signal 1252 from the OR gate 1250, and outputsa signal 1111 to the timing controller 1112. For example, if the signal1252 is at a logic high level, the falling-edge detection component 1110(e.g., a comparator) is enabled for falling edge detection; and if thesignal 1252 is at a logic low level, the falling-edge detectioncomponent 1110 (e.g., a comparator) is not enabled (e.g., is in standby)for falling edge detection. In another example, if the falling-edgedetection component 1110 (e.g., a comparator) is enabled, thefalling-edge detection component 1110 changes the signal 1111 from alogic high level to a logic low level if the signal 1158 becomes smallerthan a second threshold voltage 1113 (e.g., the second threshold voltage830, the second threshold voltage 930, and/or the second thresholdvoltage 1030). In yet another example, if the falling-edge detectioncomponent 1110 (e.g., a comparator) is not enabled, the falling-edgedetection component 1110 keeps the signal 1111 at a logic high levelregardless of whether the signal 1158 becomes smaller than the secondthreshold voltage 1113.

In another embodiment, the rising-edge detection component 1106 (e.g., acomparator) outputs a signal 1107 to the timing controller 1112. Forexample, the rising-edge detection component 1106 changes the signal1107 from a logic high level to a logic low level if the signal 1158becomes larger than a first threshold voltage 1109 (e.g., the firstthreshold voltage 828, the first threshold voltage 928, and/or the firstthreshold voltage 1028). In another example, the first threshold voltage1109 is larger than the second threshold voltage 1113 in magnitude.

In yet another embodiment, the timing controller 1112 receives thesignals 1107 and 1111 and outputs a signal 1172 to the logic controller1114. For example, the logic controller 1114 outputs a signal 1115 tothe gate driver 1116. In another example, the gate driver 1116 providesthe signal 366 (e.g., at terminal G2) to drive the transistor 310. Forexample, in response to the signal 1107 changing from a logic high levelto a logic low level, the gate driver 1116 changes the signal 366 from alogic high level to a logic low level in order to turn off thetransistor 310. In another example, if the signal 1111 changes from thelogic high level to the logic low level, the gate driver 1116 changesthe signal 366 from a logic low level to a logic high level in order toturn on the transistor 310.

According to one embodiment, the secondary controller 308 continuouslymonitors the output voltage 350 through the signal 388 (e.g., V_(s)).For example, the comparator 1124 receives a reference signal 1180 andthe signal 388 (e.g., V_(s)) and outputs a signal 1182. In anotherexample, the light-load detector 1118 receives a clock signal 1174 fromthe oscillator 1122 and a signal 1176 from the timing controller 1112.In yet another example, the signal 1176 indicates certain switchingevents (e.g., rising edges or falling edges) in the signal 362. In yetanother example, the light-load detector 1118 outputs a signal 1178which indicates the switching frequency of the power conversion system300. In yet another example, the signal generator 1120 receives thesignal 1178 and the signal 1182 and outputs a signal 1184 to the logiccontrol component 1114 in order to affect the status of the transistor310.

In another embodiment, if the output voltage 350 drops below a thresholdlevel in any conditions, for example, when the output load conditionschanges from no/light load conditions to full load conditions, theoutput voltage 350 decreases (e.g., below a threshold level). Forexample, if the signal 388 (e.g., V_(s)) changes from a first valuelarger than the reference signal 1180 in magnitude to a second valuelower than the reference signal 1180 in magnitude, the signal generator1120 generates a pulse in the signal 1184 in order to turn on thetransistor 310 during a short time period.

According to some embodiments, if the signal 1178 indicates that thepower conversion system 300 is under no/light load conditions, thesignal generator 620, in response to the signal 388 (e.g., V_(s))changing from a first value larger than the reference signal 1180 inmagnitude to a second value lower than the reference signal 1180 inmagnitude, outputs a pulse in the signal 1184. For example, in responseto the pulse in the signal 1184, the gate driver 1116 generates a pulse730 in the signal 366. In another example, the transistor 310 is turnedon during a pulse period associated with the pulse 730 in the signal366, and the channel current 368 flows in a different direction (e.g.,from the output capacitor 312 through the transistor 310 to ground). Inyet another example, the feedback signal 360 increases in magnitude, andforms a pulse. According to certain embodiments, the controller 302detects the pulse of the feedback signal 360 and, in response, increasesthe peak current of the primary winding 304 and the switching frequencyin order to deliver more energy to the secondary side. For example, theoutput voltage 350 and the voltage signal 388 increase in magnitudeeventually.

As discussed above and further emphasized here, FIG. 10 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the comparators 1230 and 1240 and thetimer component 1234 are removed from the secondary controller 308, andthe OR gate 1250 receives the signals 1216 and 1226 and outputs thesignal 1252 to the falling-edge detection component 1110 (e.g., acomparator). In another example, the comparator 1220 and the debouncecomponent 1224 are removed from the secondary controller 308, and the ORgate 1250 receives the signals 1216 and 1236 and outputs the signal 1252to the falling-edge detection component 1110 (e.g., a comparator). Inyet another example, the comparator 1210 is removed from the secondarycontroller 308, and the OR gate 1250 receives the signals 1226 and 1236and outputs the signal 1252 to the falling-edge detection component 1110(e.g., a comparator).

In yet another example, the comparators 1220, 1230 and 1240, thedebounce component 1224, the timer component 1234, and the OR gate 1250are removed from the secondary controller 308, and the signal 1216 isused as the signal 1252 and received by the falling-edge detectioncomponent 1110 (e.g., a comparator). In yet another example, thecomparators 1210, 1230 and 1240, the timer component 1234, and the ORgate 1250 are removed from the secondary controller 308, and the signal1226 is used as the signal 1252 and received by the falling-edgedetection component 1110 (e.g., a comparator). In yet another example,the comparators 1210 and 1220, the debounce component 1224, and the ORgate 1250 are removed from the secondary controller 308, and the signal1236 is used as the signal 1252 and received by the falling-edgedetection component 1110 (e.g., a comparator).

FIG. 11 is a simplified diagram showing a method for enabling thefalling-edge detection component 1110 of the secondary controller 308 aspart of the power conversion system 300 according to one embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims. One of ordinary skill in theart would recognize many variations, alternatives, and modifications.The method 1300 includes a process 1310 for keeping the falling-edgedetection component 1110 not enabled, a process 1320 for determiningwhether condition A is satisfied, a process 1322 for determining whethercondition B is satisfied, a process 1324 for determining whethercondition C is satisfied, a process 1330 for determining whether atleast one of condition A, condition B, or condition C is satisfied, anda process 1340 for enabling the falling-edge detection component 1110.

At the process 1310, the falling-edge detection component 1110 remainsnot enabled (e.g., remains in standby). For example, if the signal 1252is at a logic low level, the falling-edge detection component 1110(e.g., a comparator) is not enabled (e.g., is in standby) for fallingedge detection. In another example, if the falling-edge detectioncomponent 1110 (e.g., a comparator) is not enabled, the falling-edgedetection component 1110 keeps the signal 1111 at a logic high levelregardless of whether the signal 1158 becomes smaller than the secondthreshold voltage 1113.

At the process 1320, it is determined whether condition A is satisfied,wherein the condition A requires that the signal 1158 is larger than thefirst reference voltage 1218 (e.g., the first reference voltage 829).For example, if the signal 1158 is larger than the first referencevoltage 1218 (e.g., the first reference voltage 829), the condition A isdetermined satisfied. In another example, the process 1320 is performedby the comparator 1210.

At the process 1322, it is determined whether condition B is satisfied,wherein the condition B requires that the signal 1158 remains to belarger than the second reference voltage 1228 (e.g., the secondreference voltage 929) for a time duration that is longer than the firstthreshold time period (e.g., T_(th1)). For example, if the signal 1158remains to be larger than the second reference voltage 1228 (e.g., thesecond reference voltage 929) for a time duration that is longer thanthe first threshold time period (e.g., T_(th2)), the condition B isdetermined satisfied. In another example, the process 1322 is performedby the comparator 1220 and the debounce component 1224.

At the process 1324, it is determined whether condition C is satisfied,wherein the condition C requires that a time duration from the time whenthe voltage signal 1158 exceeds the third reference voltage 1238 (e.g.,the third reference voltage 1029) to the time when the voltage signal1158 drops below the fourth reference voltage 1248 (e.g., the fourthreference voltage 1031) is longer than the second threshold time period(e.g., T_(th2)). For example, if a time duration from the time when thevoltage signal 1158 exceeds the third reference voltage 1238 (e.g., thethird reference voltage 1029) to the time when the voltage signal 1158drops below the fourth reference voltage 1248 (e.g., the fourthreference voltage 1031) is longer than the second threshold time period(e.g., T_(th2)), the condition C is determined satisfied. In anotherexample, the process 1324 is performed by the comparators 1230 and 1240and the timer component 1234.

According to certain embodiments, the second reference voltage 1228(e.g., the second reference voltage 929) is smaller than the firstreference voltage 1218 (e.g., the first reference voltage 829), thethird reference voltage 1238 (e.g., the third reference voltage 1029) issmaller than the second reference voltage 1228 (e.g., the secondreference voltage 929), the fourth reference voltage 1248 (e.g., thefourth reference voltage 1031) is smaller than the third referencevoltage 1238 (e.g., the third reference voltage 1029), and the secondthreshold voltage 1113 (e.g., the second threshold voltage 830, thesecond threshold voltage 930, and/or the second threshold voltage 1030)is smaller than the fourth reference voltage 1248 (e.g., the fourthreference voltage 1031). According to some embodiments, the firstreference voltage 1218 (e.g., the first reference voltage 829), thesecond reference voltage 1228 (e.g., the second reference voltage 929),the third reference voltage 1238 (e.g., the third reference voltage1029), and the fourth reference voltage 1248 (e.g., the fourth referencevoltage 1031) each are larger than zero, and the second thresholdvoltage 1113 (e.g., the second threshold voltage 830, the secondthreshold voltage 930, and/or the second threshold voltage 1030) issmaller than zero.

At the process 1330, it is determined whether at least one of conditionA, condition B, or condition C is satisfied. For example, if condition Ais satisfied, at least one of condition A, condition B, or condition Cis satisfied. In another example, if condition A and condition B aresatisfied, at least one of condition A, condition B, or condition C issatisfied. In yet another example, the process 1330 is performed by theOR gate 1250.

According to one embodiment, if none of condition A, condition B, orcondition C is satisfied, the process 1310 is performed so that thefalling-edge detection component 1110 remains not enabled (e.g., remainsin standby). According to another embodiment, if at least one ofcondition A, condition B, or condition C is satisfied, the process 1340is performed.

For example, if the falling-edge detection component 1110 (e.g., acomparator) is not enabled, the falling-edge detection component 1110keeps the signal 1111 at a logic high level regardless of whether thesignal 1158 becomes smaller than the second threshold voltage 1113(e.g., the second threshold voltage 830, the second threshold voltage930, and/or the second threshold voltage 1030). In another example, ifthe falling-edge detection component 1110 (e.g., a comparator) is notenabled, the gate driver 1116 keeps the signal 366 at a logic low levelin order to keep the transistor 310 to be turned off regardless ofwhether the signal 1158 becomes smaller than the second thresholdvoltage 1113 (e.g., the second threshold voltage 830, the secondthreshold voltage 930, and/or the second threshold voltage 1030).

At the process 1340, the falling-edge detection component 1110 isenabled. For example, if the falling-edge detection component 1110(e.g., a comparator) is enabled, the falling-edge detection component1110 changes the signal 1111 from a logic high level to a logic lowlevel if the signal 1158 becomes smaller than the second thresholdvoltage 1113 (e.g., the second threshold voltage 830, the secondthreshold voltage 930, and/or the second threshold voltage 1030). Inanother example, if the signal 1111 changes from the logic high level tothe logic low level, the gate driver 1116 changes the signal 366 from alogic low level to a logic high level in order to turn on the transistor310. In yet another example, if the falling-edge detection component1110 (e.g., a comparator) is enabled and if the signal 1158 becomessmaller than the second threshold voltage 1113 (e.g., the secondthreshold voltage 830, the second threshold voltage 930, and/or thesecond threshold voltage 1030), the gate driver 1116 changes the signal366 from a logic low level to a logic high level in order to turn on thetransistor 310.

As discussed above and further emphasized here, FIG. 11 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, if the falling-edge detection component1110 is enabled at the process 1340, after the falling-edge detectioncomponent 1110 detects the signal 1158 becomes smaller than the secondthreshold voltage 1113, the falling-edge detection component 1110becomes not enabled again so that the process 1310 is repeated. Inanother example, the signal 1158 is the same as the signal 362.

In one embodiment, the secondary controller 408 is the same as thesecondary controller 308 as shown in FIG. 10 . In another embodiment,FIG. 11 is a simplified diagram showing a method for enabling thefalling-edge detection component 1110 of the secondary controller 408 aspart of the power conversion system 400.

According to some embodiments, the secondary controller 308 as part ofthe power conversion system 300 or the secondary controller 408 as partof the power conversion system 400 operating in other modes, such as acontinuous conduction mode and the critical conduction mode (e.g., thequasi-resonant mode), can also implement the scheme as illustrated inFIG. 10 and FIG. 11 .

Certain embodiments of the present invention provide a rectifyingcircuit that can avoid false firing of switching pulses due to resonantoscillation caused by parasitical capacitance and transformerinductance. For example, the false firing of switching pulses may causenon-synchronization between the secondary-side switching control and theprimary-side switching control. In another example, suchnon-synchronization can cause reliability issues that may result indamage of the power conversion system. Some embodiments of the presentinvention provide systems and methods to improve synchronization of thesecondary-side switching with the primary-side switching and alsoimprove reliability of the power conversion system. For example, asecondary controller of the present invention can identify whether thenegative pulse is a true turn-on signal or is just a resonant ringing ora glitch.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether the input signal is larger than a firstthreshold at a first time, in response to the input signal beingdetermined to be larger than the first threshold at the first time,determine whether the input signal is smaller than a second threshold ata second time, and in response to the input signal being determined tobe smaller than the second threshold at the second time, change thedrive signal at the second controller terminal from a first logic levelto a second logic level. Also, the second time is after the first time.For example, the system controller is implemented according to at leastFIG. 7 and/or FIG. 10 .

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether the input signal remains larger than afirst threshold for a time period that is longer than a predeterminedduration, and in response to the input signal being determined to haveremained larger than the first threshold for the time period that islonger than the predetermined duration, determine whether the inputsignal is smaller than a second threshold at a time following the timeperiod. Moreover, the system controller is further configured to, inresponse to the input signal being determined to be smaller than thesecond threshold at the time, change the drive signal at the secondcontroller terminal from a first logic level to a second logic level.For example, the system controller is implemented according to at leastFIG. 8 and/or FIG. 10 .

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal, and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether a time interval from a first time whenthe input signal becomes larger than a first threshold to a second timewhen the input signal becomes smaller than a second threshold is longerthan a predetermined duration, and in response to the time intervalbeing determined to be longer than the predetermined duration, determinewhether the input signal is smaller than a third threshold at a timefollowing the time interval. Also, the system controller is furtherconfigured to, in response to the input signal being determined to besmaller than the third threshold at the time, change the drive signal atthe second controller terminal from a first logic level to a secondlogic level. For example, the system controller is implemented accordingto at least FIG. 9 and/or FIG. 10 .

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminal and asecond controller terminal. Additionally, the system controller isconfigured to receive an input signal at the first controller terminal,and generate a drive signal at the second controller terminal based atleast in part on the input signal to turn on or off a transistor inorder to affect a current associated with a secondary winding of thepower conversion system. Moreover, the system controller is furtherconfigured to determine whether the input signal is larger than a firstthreshold, determine whether the input signal remains larger than asecond threshold for a time period that is longer than a firstpredetermined duration, and determine whether a time interval from afirst time when the input signal becomes larger than a third thresholdto a second time when the input signal becomes smaller than a fourththreshold is longer than a second predetermined duration. Also, thesystem controller is further configured to, in response to the inputsignal being determined to be larger than the first threshold, the inputsignal being determined to be larger than the second threshold for thetime period that is longer than the first predetermined duration, or thetime interval being determined to be longer than the secondpredetermined duration, determine whether the input signal is smallerthan a fifth threshold, and in response to the input signal beingdetermined to be smaller than the fifth threshold, change the drivesignal at the second controller terminal from a first logic level to asecond logic level. For example, the system controller is implementedaccording to at least FIG. 10 and/or FIG. 11 .

According to yet another embodiment, a method for regulating a powerconversion system includes receiving an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether the input signal is larger than a first threshold at a firsttime. Moreover, the generating a drive signal based at least in part onthe input signal to turn on or off a transistor in order to affect acurrent associated with a secondary winding of the power conversionsystem includes, in response to the input signal being determined to belarger than the first threshold at the first time, determining whetherthe input signal is smaller than a second threshold at a second time,and in response to the input signal being determined to be smaller thanthe second threshold at the second time, changing the drive signal froma first logic level to a second logic level. Also, the second time isafter the first time. For example, the method is implemented accordingto at least FIG. 7 and/or FIG. 10 .

According to yet another embodiment, a method for regulating a powerconversion system includes receiving an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether the input signal remains larger than a first threshold for atime period that is longer than a predetermined duration. Moreover, thegenerating a drive signal based at least in part on the input signal toturn on or off a transistor in order to affect a current associated witha secondary winding of the power conversion system includes, in responseto the input signal being determined to have remained larger than thefirst threshold for the time period that is longer than thepredetermined duration, determining whether the input signal is smallerthan a second threshold at a time following the time period, and inresponse to the input signal being determined to be smaller than thesecond threshold at the time, changing the drive signal from a firstlogic level to a second logic level. For example, the method isimplemented according to at least FIG. 8 and/or FIG. 10 .

According to yet another embodiment, a method for regulating a powerconversion system includes receiving an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether a time interval from a first time when the input signal becomeslarger than a first threshold to a second time when the input signalbecomes smaller than a second threshold is longer than a predeterminedduration. Moreover, the generating a drive signal based at least in parton the input signal to turn on or off a transistor in order to affect acurrent associated with a secondary winding of the power conversionsystem includes, in response to the time interval being determined to belonger than the predetermined duration, determining whether the inputsignal is smaller than a third threshold at a time following the timeinterval, and in response to the input signal being determined to besmaller than the third threshold at the time, change the drive signalfrom a first logic level to a second logic level. For example, themethod is implemented according to at least FIG. 9 and/or FIG. 10 .

According to yet another embodiment, a method for regulating a powerconversion system includes receive an input signal, processinginformation associated with the input signal, and generating a drivesignal based at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system. Additionally, the processinginformation associated with the input signal includes determiningwhether the input signal is larger than a first threshold, determiningwhether the input signal remains larger than a second threshold for atime period that is longer than a first predetermined duration, anddetermining whether a time interval from a first time when the inputsignal becomes larger than a third threshold to a second time when theinput signal becomes smaller than a fourth threshold is longer than asecond predetermined duration. Moreover, the generating a drive signalbased at least in part on the input signal to turn on or off atransistor in order to affect a current associated with a secondarywinding of the power conversion system includes, in response to theinput signal being determined to be larger than the first threshold, theinput signal being determined to be larger than the second threshold forthe time period that is longer than the first predetermined duration, orthe time interval being determined to be longer than the secondpredetermined duration, determining whether the input signal is smallerthan a fifth threshold, and in response to the input signal beingdetermined to be smaller than the fifth threshold, changing the drivesignal from a first logic level to a second logic level. For example,the method is implemented according to at least FIG. 10 and/or FIG. 11 .

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system controller for regulating a powerconversion system, the system controller comprising: a first comparatorconfigured to: receive an input signal and a first threshold; andgenerate a first comparison signal at a first logic level if the inputsignal is larger than the first threshold; a second comparatorconfigured to: receive the input signal and a second threshold; andgenerate a second comparison signal at the first logic level if theinput signal is larger than the second threshold; a debounce-signalgenerator configured to: receive the second comparison signal; generatea debounce signal at the first logic level if the second comparisonsignal remains at the first logic level for a time period that is longerthan a first predetermined duration; and generate the debounce signal ata second logic level if the second comparison signal does not remain atthe first logic level for the time period that is longer than the firstpredetermined duration; a third comparator configured to: receive theinput signal and a third threshold; and change a third comparison signalfrom the second logic level to the first logic level if the input signalbecomes larger than the third threshold; a fourth comparator configuredto: receive the input signal and a fourth threshold; and change a fourthcomparison signal from the first logic level to the second logic levelif the input signal becomes smaller than the fourth threshold; atimer-signal generator configured to: receive the third comparisonsignal and the fourth comparison signal; determine a time interval froma first time when the third comparison signal changes to the first logiclevel to a second time when the fourth comparison signal changes to thesecond logic level; if the time interval is longer than a secondpredetermined duration, generate a timer signal at the first logiclevel; and if the time interval is not longer than the secondpredetermined duration, generate the timer signal at the second logiclevel; an OR gate configured to: receive the first comparison signal,the debounce signal, and the timer signal; generate a logic signal atthe first logic level if the first comparison signal is at the firstlogic level, the debounce signal is at the first logic level, or thetimer signal is at the first logic level; and generate the logic signalat the second logic level if all of the first comparison signal, thedebounce signal and the timer signal are at the second logic level; afifth comparator configured to: receive the logic signal, the inputsignal, and a fifth threshold; in response to the logic signal being atthe first logic level, change a fifth comparison signal from the firstlogic level to the second logic level if the input signal becomessmaller than the fifth threshold; and in response to the logic signalbeing at the second logic level, keep the fifth comparison signal at thefirst logic level regardless of whether the input signal becomes smallerthan the fifth threshold; and a drive-signal generator configured tooutput a drive signal based at least in part on the fifth comparisonsignal.
 2. The system controller of claim 1 wherein: the secondthreshold is smaller than the first threshold; the third threshold issmaller than the second threshold; the fourth threshold is smaller thanthe third threshold; and the fifth threshold is smaller than the fourththreshold.
 3. The system controller of claim 2 wherein the firstthreshold, the second threshold, the third threshold, and the fourththreshold each are larger than zero.
 4. The system controller of claim 3wherein the fifth threshold is smaller than zero.
 5. The systemcontroller of claim 1 wherein: the first logic level is a logic highlevel; and the second logic level is a logic low level.
 6. The systemcontroller of claim 1 is located on a chip.